diff --git a/pkgs/test/CHANGELOG.md b/pkgs/test/CHANGELOG.md
index b988a2d..2e15457 100644
--- a/pkgs/test/CHANGELOG.md
+++ b/pkgs/test/CHANGELOG.md
@@ -8,6 +8,8 @@
   passing the `--chain-stack-traces` flag.
 * Remove `phantomjs` support completely, it was previously broken.
 * Fix `expectAsync` function type checks.
+* Add libraries `scaffolding.dart`, and `expect.dart` to allow importing a
+  subset of the normal surface area.
 
 ## 1.16.8
 
diff --git a/pkgs/test/lib/expect.dart b/pkgs/test/lib/expect.dart
new file mode 100644
index 0000000..28f64f7
--- /dev/null
+++ b/pkgs/test/lib/expect.dart
@@ -0,0 +1,5 @@
+// Copyright (c) 2021, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+export 'package:test_api/expect.dart';
diff --git a/pkgs/test/lib/scaffolding.dart b/pkgs/test/lib/scaffolding.dart
new file mode 100644
index 0000000..2712d29
--- /dev/null
+++ b/pkgs/test/lib/scaffolding.dart
@@ -0,0 +1,6 @@
+// Copyright (c) 2021, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// ignore: deprecated_member_use
+export 'package:test_core/scaffolding.dart';
diff --git a/pkgs/test/test/runner/signal_test.dart b/pkgs/test/test/runner/signal_test.dart
index 15133f2..d141329 100644
--- a/pkgs/test/test/runner/signal_test.dart
+++ b/pkgs/test/test/runner/signal_test.dart
@@ -181,41 +181,6 @@
       await signalAndQuit(test);
     });
 
-    test('causes expect() to always throw an error immediately', () async {
-      await d.file('test.dart', '''
-import 'dart:async';
-import 'dart:io';
-
-import 'package:test/test.dart';
-
-void main() {
-  var expectThrewError = false;
-
-  tearDown(() {
-    File("output").writeAsStringSync(expectThrewError.toString());
-  });
-
-  test("test", () async {
-    print("running test");
-
-    await Future.delayed(Duration(seconds: 1));
-    try {
-      expect(true, isTrue);
-    } catch (_) {
-      expectThrewError = true;
-    }
-  });
-}
-''').create();
-
-      var test = await _runTest(['test.dart']);
-      await expectLater(test.stdout, emitsThrough('running test'));
-      await signalAndQuit(test);
-
-      await d.file('output', 'true').validate();
-      expectTempDirEmpty();
-    });
-
     test('causes expectAsync() to always throw an error immediately', () async {
       await d.file('test.dart', '''
 import 'dart:async';
diff --git a/pkgs/test_api/CHANGELOG.md b/pkgs/test_api/CHANGELOG.md
index bc661ec..ec25191 100644
--- a/pkgs/test_api/CHANGELOG.md
+++ b/pkgs/test_api/CHANGELOG.md
@@ -1,5 +1,9 @@
 ## 0.4.0-dev
 
+* Add libraries `scaffolding.dart`, and `expect.dart` to allow importing as
+  subset of the normal surface area.
+* Add new APIs in `hooks.dart` to allow writing custom expectation frameworks
+  which integrate with the test runner.
 * Add examples to `throwsA` and make top-level `throws...` matchers refer to it.
 * Disable stack trace chaining by default.
 * Fix `expectAsync` function type checks.
diff --git a/pkgs/test_api/lib/expect.dart b/pkgs/test_api/lib/expect.dart
new file mode 100644
index 0000000..30a8071
--- /dev/null
+++ b/pkgs/test_api/lib/expect.dart
@@ -0,0 +1,61 @@
+// Copyright (c) 2021, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+export 'package:matcher/matcher.dart';
+
+export 'src/expect/expect.dart' show expect, expectLater, fail;
+export 'src/expect/expect_async.dart'
+    show
+        Func0,
+        Func1,
+        Func2,
+        Func3,
+        Func4,
+        Func5,
+        Func6,
+        expectAsync0,
+        expectAsync1,
+        expectAsync2,
+        expectAsync3,
+        expectAsync4,
+        expectAsync5,
+        expectAsync6,
+        expectAsyncUntil0,
+        expectAsyncUntil1,
+        expectAsyncUntil2,
+        expectAsyncUntil3,
+        expectAsyncUntil4,
+        expectAsyncUntil5,
+        expectAsyncUntil6;
+export 'src/expect/future_matchers.dart'
+    show completes, completion, doesNotComplete;
+export 'src/expect/never_called.dart' show neverCalled;
+export 'src/expect/prints_matcher.dart' show prints;
+export 'src/expect/stream_matcher.dart' show StreamMatcher;
+export 'src/expect/stream_matchers.dart'
+    show
+        emitsDone,
+        emits,
+        emitsError,
+        mayEmit,
+        emitsAnyOf,
+        emitsInOrder,
+        emitsInAnyOrder,
+        emitsThrough,
+        mayEmitMultiple,
+        neverEmits;
+export 'src/expect/throws_matcher.dart' show throwsA;
+export 'src/expect/throws_matchers.dart'
+    show
+        throwsArgumentError,
+        throwsConcurrentModificationError,
+        throwsCyclicInitializationError,
+        throwsException,
+        throwsFormatException,
+        throwsNoSuchMethodError,
+        throwsNullThrownError,
+        throwsRangeError,
+        throwsStateError,
+        throwsUnimplementedError,
+        throwsUnsupportedError;
diff --git a/pkgs/test_api/lib/hooks.dart b/pkgs/test_api/lib/hooks.dart
new file mode 100644
index 0000000..c22fe55
--- /dev/null
+++ b/pkgs/test_api/lib/hooks.dart
@@ -0,0 +1,74 @@
+// Copyright (c) 2021, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:stack_trace/stack_trace.dart';
+
+import 'src/backend/closed_exception.dart';
+import 'src/backend/invoker.dart';
+import 'src/backend/stack_trace_formatter.dart';
+
+class TestHandle {
+  /// Returns handle for the currently running test.
+  ///
+  /// This must be called from within the zone that the test is running in. If
+  /// the current zone is not a test's zone throws [OutsideTestException].
+  static TestHandle get current {
+    final invoker = Invoker.current;
+    if (invoker == null) throw OutsideTestException();
+    return TestHandle._(
+        invoker, StackTraceFormatter.current ?? _defaultFormatter);
+  }
+
+  static final _defaultFormatter = StackTraceFormatter();
+
+  final Invoker _invoker;
+  final StackTraceFormatter _stackTraceFormatter;
+  TestHandle._(this._invoker, this._stackTraceFormatter);
+
+  String get name => _invoker.liveTest.test.name;
+
+  /// Whether this test has already completed successfully.
+  ///
+  /// If a callback originating from a test case is invoked after the test has
+  /// already passed it may be an indication of a test that fails to wait for
+  /// all work to be finished, or of an asynchronous callback that is called
+  /// more times or later than expected.
+  bool get shouldBeDone => _invoker.liveTest.state.shouldBeDone;
+
+  /// Marks this test as skipped.
+  ///
+  /// A skipped test may still fail if any exception is thrown, including
+  /// uncaught asynchronous errors.
+  void markSkipped(String message) {
+    if (_invoker.closed) throw ClosedException();
+    _invoker.skip(message);
+  }
+
+  /// Indicates that this test should not be considered done until [future]
+  /// completes.
+  ///
+  /// The test may time out before [future] completes.
+  Future<T> mustWaitFor<T>(Future<T> future) {
+    if (_invoker.closed) throw ClosedException();
+    _invoker.addOutstandingCallback();
+    return future.whenComplete(_invoker.removeOutstandingCallback);
+  }
+
+  /// Converts [stackTrace] to a [Chain] according to the current test's
+  /// configuration.
+  Chain formatStackTrace(StackTrace stackTrace) =>
+      _stackTraceFormatter.formatStackTrace(stackTrace);
+}
+
+class OutsideTestException implements Exception {}
+
+/// An exception thrown when a test assertion fails.
+class TestFailure {
+  final String? message;
+
+  TestFailure(this.message);
+
+  @override
+  String toString() => message.toString();
+}
diff --git a/pkgs/test_api/lib/scaffolding.dart b/pkgs/test_api/lib/scaffolding.dart
new file mode 100644
index 0000000..4979ba3
--- /dev/null
+++ b/pkgs/test_api/lib/scaffolding.dart
@@ -0,0 +1,19 @@
+// Copyright (c) 2021, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+@Deprecated('package:test_api is not intended for general use. '
+    'Please use package:test.')
+library test_api.scaffolding;
+
+export 'src/scaffolding/on_platform.dart' show OnPlatform;
+export 'src/scaffolding/retry.dart' show Retry;
+export 'src/scaffolding/skip.dart' show Skip;
+export 'src/scaffolding/spawn_hybrid.dart' show spawnHybridUri, spawnHybridCode;
+export 'src/scaffolding/tags.dart' show Tags;
+export 'src/scaffolding/test_on.dart' show TestOn;
+export 'src/scaffolding/timeout.dart' show Timeout;
+export 'src/scaffolding/utils.dart'
+    show pumpEventQueue, printOnFailure, markTestSkipped;
+export 'src/scaffolding/test_structure.dart'
+    show group, test, setUp, setUpAll, tearDown, tearDownAll, addTearDown;
diff --git a/pkgs/test_api/lib/src/backend/declarer.dart b/pkgs/test_api/lib/src/backend/declarer.dart
index d327699..1c299ce 100644
--- a/pkgs/test_api/lib/src/backend/declarer.dart
+++ b/pkgs/test_api/lib/src/backend/declarer.dart
@@ -7,7 +7,7 @@
 import 'package:collection/collection.dart';
 import 'package:stack_trace/stack_trace.dart';
 
-import '../frontend/timeout.dart';
+import '../scaffolding/timeout.dart';
 import 'group.dart';
 import 'group_entry.dart';
 import 'invoker.dart';
diff --git a/pkgs/test_api/lib/src/backend/invoker.dart b/pkgs/test_api/lib/src/backend/invoker.dart
index 784e160..cfdc4b5 100644
--- a/pkgs/test_api/lib/src/backend/invoker.dart
+++ b/pkgs/test_api/lib/src/backend/invoker.dart
@@ -6,7 +6,7 @@
 
 import 'package:stack_trace/stack_trace.dart';
 
-import '../frontend/expect.dart';
+import '../../hooks.dart' show TestFailure;
 import '../util/pretty_print.dart';
 import 'closed_exception.dart';
 import 'declarer.dart';
diff --git a/pkgs/test_api/lib/src/backend/metadata.dart b/pkgs/test_api/lib/src/backend/metadata.dart
index 1dd90d5..ef93153 100644
--- a/pkgs/test_api/lib/src/backend/metadata.dart
+++ b/pkgs/test_api/lib/src/backend/metadata.dart
@@ -5,8 +5,8 @@
 import 'package:boolean_selector/boolean_selector.dart';
 import 'package:collection/collection.dart';
 
-import '../frontend/skip.dart';
-import '../frontend/timeout.dart';
+import '../scaffolding/skip.dart';
+import '../scaffolding/timeout.dart';
 import '../util/pretty_print.dart';
 import '../utils.dart';
 import 'platform_selector.dart';
diff --git a/pkgs/test_api/lib/src/frontend/async_matcher.dart b/pkgs/test_api/lib/src/expect/async_matcher.dart
similarity index 91%
rename from pkgs/test_api/lib/src/frontend/async_matcher.dart
rename to pkgs/test_api/lib/src/expect/async_matcher.dart
index 56ad776..236e0fd 100644
--- a/pkgs/test_api/lib/src/frontend/async_matcher.dart
+++ b/pkgs/test_api/lib/src/expect/async_matcher.dart
@@ -3,8 +3,8 @@
 // BSD-style license that can be found in the LICENSE file.
 
 import 'package:matcher/matcher.dart';
+import 'package:test_api/hooks.dart';
 
-import '../backend/invoker.dart';
 import 'expect.dart';
 
 /// A matcher that does asynchronous computation.
@@ -35,13 +35,11 @@
         reason: 'matchAsync() may only return a String, a Future, or null.');
 
     if (result is Future) {
-      Invoker.current!.addOutstandingCallback();
-      result.then((realResult) {
+      TestHandle.current.mustWaitFor(result.then((realResult) {
         if (realResult != null) {
           fail(formatFailure(this, item, realResult as String));
         }
-        Invoker.current!.removeOutstandingCallback();
-      });
+      }));
     } else if (result is String) {
       matchState[this] = result;
       return false;
diff --git a/pkgs/test_api/lib/src/frontend/expect.dart b/pkgs/test_api/lib/src/expect/expect.dart
similarity index 87%
rename from pkgs/test_api/lib/src/frontend/expect.dart
rename to pkgs/test_api/lib/src/expect/expect.dart
index 408846a..0342e87 100644
--- a/pkgs/test_api/lib/src/frontend/expect.dart
+++ b/pkgs/test_api/lib/src/expect/expect.dart
@@ -3,21 +3,10 @@
 // BSD-style license that can be found in the LICENSE file.
 
 import 'package:matcher/matcher.dart';
+import 'package:test_api/hooks.dart';
 
-import '../backend/closed_exception.dart';
-import '../backend/invoker.dart';
-import '../util/pretty_print.dart';
 import 'async_matcher.dart';
-
-/// An exception thrown when a test assertion fails.
-class TestFailure {
-  final String? message;
-
-  TestFailure(this.message);
-
-  @override
-  String toString() => message.toString();
-}
+import 'util/pretty_print.dart';
 
 /// The type used for functions that can be used to build up error reports
 /// upon failures in [expect].
@@ -78,6 +67,7 @@
 // ignore: body_might_complete_normally
 Future _expect(actual, matcher,
     {String? reason, skip, bool verbose = false, ErrorFormatter? formatter}) {
+  final test = TestHandle.current;
   formatter ??= (actual, matcher, reason, matchState, verbose) {
     var mismatchDescription = StringDescription();
     matcher.describeMismatch(actual, mismatchDescription, matchState, verbose);
@@ -86,12 +76,6 @@
         reason: reason);
   };
 
-  if (Invoker.current == null) {
-    throw StateError('expect() may only be called within a test.');
-  }
-
-  if (Invoker.current!.closed) throw ClosedException();
-
   if (skip != null && skip is! bool && skip is! String) {
     throw ArgumentError.value(skip, 'skip', 'must be a bool or a String');
   }
@@ -108,7 +92,7 @@
       message = 'Skip expect ($description).';
     }
 
-    Invoker.current!.skip(message);
+    test.markSkipped(message);
     return Future.sync(() {});
   }
 
@@ -122,16 +106,11 @@
     if (result is String) {
       fail(formatFailure(matcher, actual, result, reason: reason));
     } else if (result is Future) {
-      Invoker.current!.addOutstandingCallback();
-      return result.then((realResult) {
+      return test.mustWaitFor(result.then((realResult) {
         if (realResult == null) return;
         fail(formatFailure(matcher as Matcher, actual, realResult as String,
             reason: reason));
-      }).whenComplete(() {
-        // Always remove this, in case the failure is caught and handled
-        // gracefully.
-        Invoker.current!.removeOutstandingCallback();
-      });
+      }));
     }
 
     return Future.sync(() {});
diff --git a/pkgs/test_api/lib/src/frontend/expect_async.dart b/pkgs/test_api/lib/src/expect/expect_async.dart
similarity index 80%
rename from pkgs/test_api/lib/src/frontend/expect_async.dart
rename to pkgs/test_api/lib/src/expect/expect_async.dart
index 95ab80a..e326e47 100644
--- a/pkgs/test_api/lib/src/frontend/expect_async.dart
+++ b/pkgs/test_api/lib/src/expect/expect_async.dart
@@ -4,9 +4,9 @@
 
 import 'dart:async';
 
-import '../backend/invoker.dart';
-import '../util/placeholder.dart';
-import 'expect.dart';
+import 'package:test_api/hooks.dart';
+
+import 'util/placeholder.dart';
 
 // Function types returned by expectAsync# methods.
 
@@ -61,15 +61,14 @@
   /// The number of times the function has been called.
   int _actualCalls = 0;
 
-  /// The test invoker in which this function was wrapped.
-  Invoker? get _invoker => _zone[#test.invoker] as Invoker?;
-
-  /// The zone in which this function was wrapped.
-  final Zone _zone;
+  /// The test in which this function was wrapped.
+  late final TestHandle _test;
 
   /// Whether this function has been called the requisite number of times.
   late bool _complete;
 
+  Completer<void>? _expectationSatisfied;
+
   /// Wraps [callback] in a function that asserts that it's called at least
   /// [minExpected] times and no more than [maxExpected] times.
   ///
@@ -84,17 +83,21 @@
             (maxExpected == 0 && minExpected > 0) ? minExpected : maxExpected,
         _isDone = isDone,
         _reason = reason == null ? '' : '\n$reason',
-        _zone = Zone.current,
         _id = _makeCallbackId(id, callback) {
-    if (_invoker == null) {
-      throw StateError('[expectAsync] was called outside of a test.');
-    } else if (maxExpected > 0 && minExpected > maxExpected) {
+    try {
+      _test = TestHandle.current;
+    } on OutsideTestException {
+      throw StateError('`expectAsync` must be called within a test.');
+    }
+
+    if (maxExpected > 0 && minExpected > maxExpected) {
       throw ArgumentError('max ($maxExpected) may not be less than count '
           '($minExpected).');
     }
 
     if (isDone != null || minExpected > 0) {
-      _invoker!.addOutstandingCallback();
+      var completer = _expectationSatisfied = Completer<void>();
+      _test.mustWaitFor(completer.future);
       _complete = false;
     } else {
       _complete = true;
@@ -134,7 +137,7 @@
     if (_callback is Function(Never)) return max1;
     if (_callback is Function()) return max0;
 
-    _invoker!.removeOutstandingCallback();
+    _expectationSatisfied?.complete();
     throw ArgumentError(
         'The wrapped function has more than 6 required arguments');
   }
@@ -184,9 +187,9 @@
     // pass it to the invoker anyway.
     try {
       _actualCalls++;
-      if (_invoker!.liveTest.state.shouldBeDone) {
+      if (_test.shouldBeDone) {
         throw 'Callback ${_id}called ($_actualCalls) after test case '
-            '${_invoker!.liveTest.test.name} had already completed.$_reason';
+            '${_test.name} had already completed.$_reason';
       } else if (_maxExpectedCalls >= 0 && _actualCalls > _maxExpectedCalls) {
         throw TestFailure('Callback ${_id}called more times than expected '
             '($_maxExpectedCalls).$_reason');
@@ -207,7 +210,7 @@
     // Mark this callback as complete and remove it from the test case's
     // oustanding callback count; if that hits zero the test is done.
     _complete = true;
-    _invoker!.removeOutstandingCallback();
+    _expectationSatisfied?.complete();
   }
 }
 
@@ -217,13 +220,8 @@
 /// [expectAsync6] instead.
 @Deprecated('Will be removed in 0.13.0')
 Function expectAsync(Function callback,
-    {int count = 1, int max = 0, String? id, String? reason}) {
-  if (Invoker.current == null) {
-    throw StateError('expectAsync() may only be called within a test.');
-  }
-
-  return _ExpectedFunction(callback, count, max, id: id, reason: reason).func;
-}
+        {int count = 1, int max = 0, String? id, String? reason}) =>
+    _ExpectedFunction(callback, count, max, id: id, reason: reason).func;
 
 /// Informs the framework that the given [callback] of arity 0 is expected to be
 /// called [count] number of times (by default 1).
@@ -247,14 +245,8 @@
 /// [expectAsync1], [expectAsync2], [expectAsync3], [expectAsync4],
 /// [expectAsync5], and [expectAsync6] for callbacks with different arity.
 Func0<T> expectAsync0<T>(T Function() callback,
-    {int count = 1, int max = 0, String? id, String? reason}) {
-  if (Invoker.current == null) {
-    throw StateError('expectAsync0() may only be called within a test.');
-  }
-
-  return _ExpectedFunction<T>(callback, count, max, id: id, reason: reason)
-      .max0;
-}
+        {int count = 1, int max = 0, String? id, String? reason}) =>
+    _ExpectedFunction<T>(callback, count, max, id: id, reason: reason).max0;
 
 /// Informs the framework that the given [callback] of arity 1 is expected to be
 /// called [count] number of times (by default 1).
@@ -278,14 +270,8 @@
 /// [expectAsync0], [expectAsync2], [expectAsync3], [expectAsync4],
 /// [expectAsync5], and [expectAsync6] for callbacks with different arity.
 Func1<T, A> expectAsync1<T, A>(T Function(A) callback,
-    {int count = 1, int max = 0, String? id, String? reason}) {
-  if (Invoker.current == null) {
-    throw StateError('expectAsync1() may only be called within a test.');
-  }
-
-  return _ExpectedFunction<T>(callback, count, max, id: id, reason: reason)
-      .max1;
-}
+        {int count = 1, int max = 0, String? id, String? reason}) =>
+    _ExpectedFunction<T>(callback, count, max, id: id, reason: reason).max1;
 
 /// Informs the framework that the given [callback] of arity 2 is expected to be
 /// called [count] number of times (by default 1).
@@ -309,14 +295,8 @@
 /// [expectAsync0], [expectAsync1], [expectAsync3], [expectAsync4],
 /// [expectAsync5], and [expectAsync6] for callbacks with different arity.
 Func2<T, A, B> expectAsync2<T, A, B>(T Function(A, B) callback,
-    {int count = 1, int max = 0, String? id, String? reason}) {
-  if (Invoker.current == null) {
-    throw StateError('expectAsync2() may only be called within a test.');
-  }
-
-  return _ExpectedFunction<T>(callback, count, max, id: id, reason: reason)
-      .max2;
-}
+        {int count = 1, int max = 0, String? id, String? reason}) =>
+    _ExpectedFunction<T>(callback, count, max, id: id, reason: reason).max2;
 
 /// Informs the framework that the given [callback] of arity 3 is expected to be
 /// called [count] number of times (by default 1).
@@ -340,14 +320,8 @@
 /// [expectAsync0], [expectAsync1], [expectAsync2], [expectAsync4],
 /// [expectAsync5], and [expectAsync6] for callbacks with different arity.
 Func3<T, A, B, C> expectAsync3<T, A, B, C>(T Function(A, B, C) callback,
-    {int count = 1, int max = 0, String? id, String? reason}) {
-  if (Invoker.current == null) {
-    throw StateError('expectAsync3() may only be called within a test.');
-  }
-
-  return _ExpectedFunction<T>(callback, count, max, id: id, reason: reason)
-      .max3;
-}
+        {int count = 1, int max = 0, String? id, String? reason}) =>
+    _ExpectedFunction<T>(callback, count, max, id: id, reason: reason).max3;
 
 /// Informs the framework that the given [callback] of arity 4 is expected to be
 /// called [count] number of times (by default 1).
@@ -371,18 +345,12 @@
 /// [expectAsync0], [expectAsync1], [expectAsync2], [expectAsync3],
 /// [expectAsync5], and [expectAsync6] for callbacks with different arity.
 Func4<T, A, B, C, D> expectAsync4<T, A, B, C, D>(
-    T Function(A, B, C, D) callback,
-    {int count = 1,
-    int max = 0,
-    String? id,
-    String? reason}) {
-  if (Invoker.current == null) {
-    throw StateError('expectAsync4() may only be called within a test.');
-  }
-
-  return _ExpectedFunction<T>(callback, count, max, id: id, reason: reason)
-      .max4;
-}
+        T Function(A, B, C, D) callback,
+        {int count = 1,
+        int max = 0,
+        String? id,
+        String? reason}) =>
+    _ExpectedFunction<T>(callback, count, max, id: id, reason: reason).max4;
 
 /// Informs the framework that the given [callback] of arity 5 is expected to be
 /// called [count] number of times (by default 1).
@@ -406,18 +374,12 @@
 /// [expectAsync0], [expectAsync1], [expectAsync2], [expectAsync3],
 /// [expectAsync4], and [expectAsync6] for callbacks with different arity.
 Func5<T, A, B, C, D, E> expectAsync5<T, A, B, C, D, E>(
-    T Function(A, B, C, D, E) callback,
-    {int count = 1,
-    int max = 0,
-    String? id,
-    String? reason}) {
-  if (Invoker.current == null) {
-    throw StateError('expectAsync5() may only be called within a test.');
-  }
-
-  return _ExpectedFunction<T>(callback, count, max, id: id, reason: reason)
-      .max5;
-}
+        T Function(A, B, C, D, E) callback,
+        {int count = 1,
+        int max = 0,
+        String? id,
+        String? reason}) =>
+    _ExpectedFunction<T>(callback, count, max, id: id, reason: reason).max5;
 
 /// Informs the framework that the given [callback] of arity 6 is expected to be
 /// called [count] number of times (by default 1).
@@ -441,18 +403,12 @@
 /// [expectAsync0], [expectAsync1], [expectAsync2], [expectAsync3],
 /// [expectAsync4], and [expectAsync5] for callbacks with different arity.
 Func6<T, A, B, C, D, E, F> expectAsync6<T, A, B, C, D, E, F>(
-    T Function(A, B, C, D, E, F) callback,
-    {int count = 1,
-    int max = 0,
-    String? id,
-    String? reason}) {
-  if (Invoker.current == null) {
-    throw StateError('expectAsync6() may only be called within a test.');
-  }
-
-  return _ExpectedFunction<T>(callback, count, max, id: id, reason: reason)
-      .max6;
-}
+        T Function(A, B, C, D, E, F) callback,
+        {int count = 1,
+        int max = 0,
+        String? id,
+        String? reason}) =>
+    _ExpectedFunction<T>(callback, count, max, id: id, reason: reason).max6;
 
 /// This function is deprecated because it doesn't work well with strong mode.
 /// Use [expectAsyncUntil0], [expectAsyncUntil1],
@@ -460,15 +416,9 @@
 /// [expectAsyncUntil5], or [expectAsyncUntil6] instead.
 @Deprecated('Will be removed in 0.13.0')
 Function expectAsyncUntil(Function callback, bool Function() isDone,
-    {String? id, String? reason}) {
-  if (Invoker.current == null) {
-    throw StateError('expectAsyncUntil() may only be called within a test.');
-  }
-
-  return _ExpectedFunction(callback, 0, -1,
-          id: id, reason: reason, isDone: isDone)
-      .func;
-}
+        {String? id, String? reason}) =>
+    _ExpectedFunction(callback, 0, -1, id: id, reason: reason, isDone: isDone)
+        .func;
 
 /// Informs the framework that the given [callback] of arity 0 is expected to be
 /// called until [isDone] returns true.
@@ -488,15 +438,10 @@
 /// [expectAsyncUntil4], [expectAsyncUntil5], and [expectAsyncUntil6] for
 /// callbacks with different arity.
 Func0<T> expectAsyncUntil0<T>(T Function() callback, bool Function() isDone,
-    {String? id, String? reason}) {
-  if (Invoker.current == null) {
-    throw StateError('expectAsyncUntil0() may only be called within a test.');
-  }
-
-  return _ExpectedFunction<T>(callback, 0, -1,
-          id: id, reason: reason, isDone: isDone)
-      .max0;
-}
+        {String? id, String? reason}) =>
+    _ExpectedFunction<T>(callback, 0, -1,
+            id: id, reason: reason, isDone: isDone)
+        .max0;
 
 /// Informs the framework that the given [callback] of arity 1 is expected to be
 /// called until [isDone] returns true.
@@ -516,16 +461,11 @@
 /// [expectAsyncUntil4], [expectAsyncUntil5], and [expectAsyncUntil6] for
 /// callbacks with different arity.
 Func1<T, A> expectAsyncUntil1<T, A>(
-    T Function(A) callback, bool Function() isDone,
-    {String? id, String? reason}) {
-  if (Invoker.current == null) {
-    throw StateError('expectAsyncUntil1() may only be called within a test.');
-  }
-
-  return _ExpectedFunction<T>(callback, 0, -1,
-          id: id, reason: reason, isDone: isDone)
-      .max1;
-}
+        T Function(A) callback, bool Function() isDone,
+        {String? id, String? reason}) =>
+    _ExpectedFunction<T>(callback, 0, -1,
+            id: id, reason: reason, isDone: isDone)
+        .max1;
 
 /// Informs the framework that the given [callback] of arity 2 is expected to be
 /// called until [isDone] returns true.
@@ -545,16 +485,11 @@
 /// [expectAsyncUntil4], [expectAsyncUntil5], and [expectAsyncUntil6] for
 /// callbacks with different arity.
 Func2<T, A, B> expectAsyncUntil2<T, A, B>(
-    T Function(A, B) callback, bool Function() isDone,
-    {String? id, String? reason}) {
-  if (Invoker.current == null) {
-    throw StateError('expectAsyncUntil2() may only be called within a test.');
-  }
-
-  return _ExpectedFunction<T>(callback, 0, -1,
-          id: id, reason: reason, isDone: isDone)
-      .max2;
-}
+        T Function(A, B) callback, bool Function() isDone,
+        {String? id, String? reason}) =>
+    _ExpectedFunction<T>(callback, 0, -1,
+            id: id, reason: reason, isDone: isDone)
+        .max2;
 
 /// Informs the framework that the given [callback] of arity 3 is expected to be
 /// called until [isDone] returns true.
@@ -574,16 +509,11 @@
 /// [expectAsyncUntil4], [expectAsyncUntil5], and [expectAsyncUntil6] for
 /// callbacks with different arity.
 Func3<T, A, B, C> expectAsyncUntil3<T, A, B, C>(
-    T Function(A, B, C) callback, bool Function() isDone,
-    {String? id, String? reason}) {
-  if (Invoker.current == null) {
-    throw StateError('expectAsyncUntil3() may only be called within a test.');
-  }
-
-  return _ExpectedFunction<T>(callback, 0, -1,
-          id: id, reason: reason, isDone: isDone)
-      .max3;
-}
+        T Function(A, B, C) callback, bool Function() isDone,
+        {String? id, String? reason}) =>
+    _ExpectedFunction<T>(callback, 0, -1,
+            id: id, reason: reason, isDone: isDone)
+        .max3;
 
 /// Informs the framework that the given [callback] of arity 4 is expected to be
 /// called until [isDone] returns true.
@@ -603,16 +533,11 @@
 /// [expectAsyncUntil3], [expectAsyncUntil5], and [expectAsyncUntil6] for
 /// callbacks with different arity.
 Func4<T, A, B, C, D> expectAsyncUntil4<T, A, B, C, D>(
-    T Function(A, B, C, D) callback, bool Function() isDone,
-    {String? id, String? reason}) {
-  if (Invoker.current == null) {
-    throw StateError('expectAsyncUntil4() may only be called within a test.');
-  }
-
-  return _ExpectedFunction<T>(callback, 0, -1,
-          id: id, reason: reason, isDone: isDone)
-      .max4;
-}
+        T Function(A, B, C, D) callback, bool Function() isDone,
+        {String? id, String? reason}) =>
+    _ExpectedFunction<T>(callback, 0, -1,
+            id: id, reason: reason, isDone: isDone)
+        .max4;
 
 /// Informs the framework that the given [callback] of arity 5 is expected to be
 /// called until [isDone] returns true.
@@ -632,16 +557,11 @@
 /// [expectAsyncUntil3], [expectAsyncUntil4], and [expectAsyncUntil6] for
 /// callbacks with different arity.
 Func5<T, A, B, C, D, E> expectAsyncUntil5<T, A, B, C, D, E>(
-    T Function(A, B, C, D, E) callback, bool Function() isDone,
-    {String? id, String? reason}) {
-  if (Invoker.current == null) {
-    throw StateError('expectAsyncUntil5() may only be called within a test.');
-  }
-
-  return _ExpectedFunction<T>(callback, 0, -1,
-          id: id, reason: reason, isDone: isDone)
-      .max5;
-}
+        T Function(A, B, C, D, E) callback, bool Function() isDone,
+        {String? id, String? reason}) =>
+    _ExpectedFunction<T>(callback, 0, -1,
+            id: id, reason: reason, isDone: isDone)
+        .max5;
 
 /// Informs the framework that the given [callback] of arity 6 is expected to be
 /// called until [isDone] returns true.
@@ -661,13 +581,8 @@
 /// [expectAsyncUntil3], [expectAsyncUntil4], and [expectAsyncUntil5] for
 /// callbacks with different arity.
 Func6<T, A, B, C, D, E, F> expectAsyncUntil6<T, A, B, C, D, E, F>(
-    T Function(A, B, C, D, E, F) callback, bool Function() isDone,
-    {String? id, String? reason}) {
-  if (Invoker.current == null) {
-    throw StateError('expectAsyncUntil() may only be called within a test.');
-  }
-
-  return _ExpectedFunction<T>(callback, 0, -1,
-          id: id, reason: reason, isDone: isDone)
-      .max6;
-}
+        T Function(A, B, C, D, E, F) callback, bool Function() isDone,
+        {String? id, String? reason}) =>
+    _ExpectedFunction<T>(callback, 0, -1,
+            id: id, reason: reason, isDone: isDone)
+        .max6;
diff --git a/pkgs/test_api/lib/src/frontend/future_matchers.dart b/pkgs/test_api/lib/src/expect/future_matchers.dart
similarity index 97%
rename from pkgs/test_api/lib/src/frontend/future_matchers.dart
rename to pkgs/test_api/lib/src/expect/future_matchers.dart
index 2a2e186..d6d39c0 100644
--- a/pkgs/test_api/lib/src/frontend/future_matchers.dart
+++ b/pkgs/test_api/lib/src/expect/future_matchers.dart
@@ -3,11 +3,11 @@
 // BSD-style license that can be found in the LICENSE file.
 
 import 'package:matcher/matcher.dart';
+import 'package:test_api/test_api.dart' show pumpEventQueue;
 
-import '../util/pretty_print.dart';
 import 'async_matcher.dart';
 import 'expect.dart';
-import 'utils.dart';
+import 'util/pretty_print.dart';
 
 /// Matches a [Future] that completes successfully with any value.
 ///
diff --git a/pkgs/test_api/lib/src/frontend/never_called.dart b/pkgs/test_api/lib/src/expect/never_called.dart
similarity index 91%
rename from pkgs/test_api/lib/src/frontend/never_called.dart
rename to pkgs/test_api/lib/src/expect/never_called.dart
index fadbeff..d950650 100644
--- a/pkgs/test_api/lib/src/frontend/never_called.dart
+++ b/pkgs/test_api/lib/src/expect/never_called.dart
@@ -5,12 +5,13 @@
 import 'dart:async';
 
 import 'package:stack_trace/stack_trace.dart';
+import 'package:test_api/hooks.dart';
+import 'package:test_api/test_api.dart' show pumpEventQueue;
 
-import '../util/placeholder.dart';
-import '../util/pretty_print.dart';
 import 'expect.dart';
 import 'future_matchers.dart';
-import 'utils.dart';
+import 'util/placeholder.dart';
+import 'util/pretty_print.dart';
 
 /// Returns a function that causes the test to fail if it's called.
 ///
diff --git a/pkgs/test_api/lib/src/frontend/prints_matcher.dart b/pkgs/test_api/lib/src/expect/prints_matcher.dart
similarity index 98%
rename from pkgs/test_api/lib/src/frontend/prints_matcher.dart
rename to pkgs/test_api/lib/src/expect/prints_matcher.dart
index 5c6fd52..5e9769b 100644
--- a/pkgs/test_api/lib/src/frontend/prints_matcher.dart
+++ b/pkgs/test_api/lib/src/expect/prints_matcher.dart
@@ -6,9 +6,9 @@
 
 import 'package:matcher/matcher.dart';
 
-import '../util/pretty_print.dart';
 import 'async_matcher.dart';
 import 'expect.dart';
+import 'util/pretty_print.dart';
 
 /// Matches a [Function] that prints text that matches [matcher].
 ///
diff --git a/pkgs/test_api/lib/src/frontend/stream_matcher.dart b/pkgs/test_api/lib/src/expect/stream_matcher.dart
similarity index 97%
rename from pkgs/test_api/lib/src/frontend/stream_matcher.dart
rename to pkgs/test_api/lib/src/expect/stream_matcher.dart
index adc2a40..78d5a3a 100644
--- a/pkgs/test_api/lib/src/frontend/stream_matcher.dart
+++ b/pkgs/test_api/lib/src/expect/stream_matcher.dart
@@ -4,10 +4,10 @@
 
 import 'package:async/async.dart';
 import 'package:matcher/matcher.dart';
+import 'package:test_api/hooks.dart';
 
-import '../util/pretty_print.dart';
 import 'async_matcher.dart';
-import 'format_stack_trace.dart';
+import 'util/pretty_print.dart';
 
 /// A matcher that matches events from [Stream]s or [StreamQueue]s.
 ///
@@ -164,7 +164,7 @@
           return addBullet(event.asValue!.value.toString());
         } else {
           var error = event.asError!;
-          var chain = formatStackTrace(error.stackTrace);
+          var chain = TestHandle.current.formatStackTrace(error.stackTrace);
           var text = '${error.error}\n$chain';
           return indent(text, first: '! ');
         }
diff --git a/pkgs/test_api/lib/src/frontend/stream_matchers.dart b/pkgs/test_api/lib/src/expect/stream_matchers.dart
similarity index 99%
rename from pkgs/test_api/lib/src/frontend/stream_matchers.dart
rename to pkgs/test_api/lib/src/expect/stream_matchers.dart
index 1e4ce96..95495ff 100644
--- a/pkgs/test_api/lib/src/frontend/stream_matchers.dart
+++ b/pkgs/test_api/lib/src/expect/stream_matchers.dart
@@ -5,10 +5,10 @@
 import 'package:async/async.dart';
 import 'package:matcher/matcher.dart';
 
-import '../util/pretty_print.dart';
 import 'async_matcher.dart';
 import 'stream_matcher.dart';
 import 'throws_matcher.dart';
+import 'util/pretty_print.dart';
 
 /// Returns a [StreamMatcher] that asserts that the stream emits a "done" event.
 final emitsDone = StreamMatcher(
diff --git a/pkgs/test_api/lib/src/frontend/throws_matcher.dart b/pkgs/test_api/lib/src/expect/throws_matcher.dart
similarity index 95%
rename from pkgs/test_api/lib/src/frontend/throws_matcher.dart
rename to pkgs/test_api/lib/src/expect/throws_matcher.dart
index ab97408..b4f081e 100644
--- a/pkgs/test_api/lib/src/frontend/throws_matcher.dart
+++ b/pkgs/test_api/lib/src/expect/throws_matcher.dart
@@ -3,10 +3,10 @@
 // BSD-style license that can be found in the LICENSE file.
 
 import 'package:matcher/matcher.dart';
+import 'package:test_api/hooks.dart';
 
-import '../util/pretty_print.dart';
 import 'async_matcher.dart';
-import 'format_stack_trace.dart';
+import 'util/pretty_print.dart';
 
 /// This function is deprecated.
 ///
@@ -125,8 +125,9 @@
     var buffer = StringBuffer();
     buffer.writeln(indent(prettyPrint(error), first: 'threw '));
     if (trace != null) {
-      buffer
-          .writeln(indent(formatStackTrace(trace).toString(), first: 'stack '));
+      buffer.writeln(indent(
+          TestHandle.current.formatStackTrace(trace).toString(),
+          first: 'stack '));
     }
     if (result.isNotEmpty) buffer.writeln(indent(result, first: 'which '));
     return buffer.toString().trimRight();
diff --git a/pkgs/test_api/lib/src/frontend/throws_matchers.dart b/pkgs/test_api/lib/src/expect/throws_matchers.dart
similarity index 100%
rename from pkgs/test_api/lib/src/frontend/throws_matchers.dart
rename to pkgs/test_api/lib/src/expect/throws_matchers.dart
diff --git a/pkgs/test_api/lib/src/util/placeholder.dart b/pkgs/test_api/lib/src/expect/util/placeholder.dart
similarity index 100%
rename from pkgs/test_api/lib/src/util/placeholder.dart
rename to pkgs/test_api/lib/src/expect/util/placeholder.dart
diff --git a/pkgs/test_api/lib/src/expect/util/pretty_print.dart b/pkgs/test_api/lib/src/expect/util/pretty_print.dart
new file mode 100644
index 0000000..f21399d
--- /dev/null
+++ b/pkgs/test_api/lib/src/expect/util/pretty_print.dart
@@ -0,0 +1,47 @@
+// Copyright (c) 2021, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:matcher/matcher.dart';
+import 'package:term_glyph/term_glyph.dart' as glyph;
+
+/// Indent each line in [string] by [first.length] spaces.
+///
+/// [first] is used in place of the first line's indentation.
+String indent(String text, {required String first}) {
+  final prefix = ' ' * first.length;
+  var lines = text.split('\n');
+  if (lines.length == 1) return '$first$text';
+
+  var buffer = StringBuffer('$first${lines.first}\n');
+
+  // Write out all but the first and last lines with [prefix].
+  for (var line in lines.skip(1).take(lines.length - 2)) {
+    buffer.writeln('$prefix$line');
+  }
+  buffer.write('$prefix${lines.last}');
+  return buffer.toString();
+}
+
+/// Returns a pretty-printed representation of [value].
+///
+/// The matcher package doesn't expose its pretty-print function directly, but
+/// we can use it through StringDescription.
+String prettyPrint(value) =>
+    StringDescription().addDescriptionOf(value).toString();
+
+/// Indents [text], and adds a bullet at the beginning.
+String addBullet(String text) => indent(text, first: '${glyph.bullet} ');
+
+/// Converts [strings] to a bulleted list.
+String bullet(Iterable<String> strings) => strings.map(addBullet).join('\n');
+
+/// Returns [name] if [number] is 1, or the plural of [name] otherwise.
+///
+/// By default, this just adds "s" to the end of [name] to get the plural. If
+/// [plural] is passed, that's used instead.
+String pluralize(String name, int number, {String? plural}) {
+  if (number == 1) return name;
+  if (plural != null) return plural;
+  return '${name}s';
+}
diff --git a/pkgs/test_api/lib/src/frontend/format_stack_trace.dart b/pkgs/test_api/lib/src/frontend/format_stack_trace.dart
deleted file mode 100644
index b6eee2b..0000000
--- a/pkgs/test_api/lib/src/frontend/format_stack_trace.dart
+++ /dev/null
@@ -1,22 +0,0 @@
-// Copyright (c) 2017, the Dart project authors.  Please see the AUTHORS file
-// for details. All rights reserved. Use of this source code is governed by a
-// BSD-style license that can be found in the LICENSE file.
-
-import 'package:stack_trace/stack_trace.dart';
-
-import '../backend/stack_trace_formatter.dart';
-
-/// The default formatter to use for formatting stack traces.
-///
-/// This is used in situations where the zone-scoped formatter is unavailable,
-/// such as when running via `dart path/to/test.dart'.
-final _defaultFormatter = StackTraceFormatter();
-
-/// Converts [stackTrace] to a [Chain] according to the current test's
-/// configuration.
-///
-/// If [verbose] is `true`, this doesn't fold out irrelevant stack frames. It
-/// defaults to the current test's `verbose_trace` configuration.
-Chain formatStackTrace(StackTrace stackTrace, {bool? verbose}) =>
-    (StackTraceFormatter.current ?? _defaultFormatter)
-        .formatStackTrace(stackTrace, verbose: verbose);
diff --git a/pkgs/test_api/lib/src/frontend/utils.dart b/pkgs/test_api/lib/src/frontend/utils.dart
deleted file mode 100644
index ac023e5..0000000
--- a/pkgs/test_api/lib/src/frontend/utils.dart
+++ /dev/null
@@ -1,16 +0,0 @@
-// Copyright (c) 2017, the Dart project authors.  Please see the AUTHORS file
-// for details. All rights reserved. Use of this source code is governed by a
-// BSD-style license that can be found in the LICENSE file.
-
-/// Returns a [Future] that completes after the [event loop][] has run the given
-/// number of [times] (20 by default).
-///
-/// [event loop]: https://medium.com/dartlang/dart-asynchronous-programming-isolates-and-event-loops-bffc3e296a6a
-///
-/// Awaiting this approximates waiting until all asynchronous work (other than
-/// work that's waiting for external resources) completes.
-Future pumpEventQueue({int times = 20}) {
-  if (times == 0) return Future.value();
-  // Use the event loop to allow the microtask queue to finish.
-  return Future(() => pumpEventQueue(times: times - 1));
-}
diff --git a/pkgs/test_api/lib/src/frontend/on_platform.dart b/pkgs/test_api/lib/src/scaffolding/on_platform.dart
similarity index 100%
rename from pkgs/test_api/lib/src/frontend/on_platform.dart
rename to pkgs/test_api/lib/src/scaffolding/on_platform.dart
diff --git a/pkgs/test_api/lib/src/frontend/retry.dart b/pkgs/test_api/lib/src/scaffolding/retry.dart
similarity index 100%
rename from pkgs/test_api/lib/src/frontend/retry.dart
rename to pkgs/test_api/lib/src/scaffolding/retry.dart
diff --git a/pkgs/test_api/lib/src/frontend/skip.dart b/pkgs/test_api/lib/src/scaffolding/skip.dart
similarity index 100%
rename from pkgs/test_api/lib/src/frontend/skip.dart
rename to pkgs/test_api/lib/src/scaffolding/skip.dart
diff --git a/pkgs/test_api/lib/src/frontend/spawn_hybrid.dart b/pkgs/test_api/lib/src/scaffolding/spawn_hybrid.dart
similarity index 100%
rename from pkgs/test_api/lib/src/frontend/spawn_hybrid.dart
rename to pkgs/test_api/lib/src/scaffolding/spawn_hybrid.dart
diff --git a/pkgs/test_api/lib/src/frontend/tags.dart b/pkgs/test_api/lib/src/scaffolding/tags.dart
similarity index 100%
rename from pkgs/test_api/lib/src/frontend/tags.dart
rename to pkgs/test_api/lib/src/scaffolding/tags.dart
diff --git a/pkgs/test_api/lib/src/frontend/test_on.dart b/pkgs/test_api/lib/src/scaffolding/test_on.dart
similarity index 100%
rename from pkgs/test_api/lib/src/frontend/test_on.dart
rename to pkgs/test_api/lib/src/scaffolding/test_on.dart
diff --git a/pkgs/test_api/lib/src/scaffolding/test_structure.dart b/pkgs/test_api/lib/src/scaffolding/test_structure.dart
new file mode 100644
index 0000000..1a99435
--- /dev/null
+++ b/pkgs/test_api/lib/src/scaffolding/test_structure.dart
@@ -0,0 +1,249 @@
+// Copyright (c) 2021, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:async';
+
+import 'package:meta/meta.dart';
+
+import '../backend/declarer.dart';
+import '../backend/invoker.dart';
+import '../scaffolding/timeout.dart';
+
+// test_core does not support running tests directly, so the Declarer should
+// always be on the Zone.
+Declarer get _declarer => Zone.current[#test.declarer] as Declarer;
+
+// TODO(nweiz): This and other top-level functions should throw exceptions if
+// they're called after the declarer has finished declaring.
+/// Creates a new test case with the given description (converted to a string)
+/// and body.
+///
+/// The description will be added to the descriptions of any surrounding
+/// [group]s. If [testOn] is passed, it's parsed as a [platform selector][]; the
+/// test will only be run on matching platforms.
+///
+/// [platform selector]: https://github.com/dart-lang/test/tree/master/pkgs/test#platform-selectors
+///
+/// If [timeout] is passed, it's used to modify or replace the default timeout
+/// of 30 seconds. Timeout modifications take precedence in suite-group-test
+/// order, so [timeout] will also modify any timeouts set on the group or suite.
+///
+/// If [skip] is a String or `true`, the test is skipped. If it's a String, it
+/// should explain why the test is skipped; this reason will be printed instead
+/// of running the test.
+///
+/// If [tags] is passed, it declares user-defined tags that are applied to the
+/// test. These tags can be used to select or skip the test on the command line,
+/// or to do bulk test configuration. All tags should be declared in the
+/// [package configuration file][configuring tags]. The parameter can be an
+/// [Iterable] of tag names, or a [String] representing a single tag.
+///
+/// If [retry] is passed, the test will be retried the provided number of times
+/// before being marked as a failure.
+///
+/// [configuring tags]: https://github.com/dart-lang/test/blob/master/doc/package_config.md#configuring-tags
+///
+/// [onPlatform] allows tests to be configured on a platform-by-platform
+/// basis. It's a map from strings that are parsed as [PlatformSelector]s to
+/// annotation classes: [Timeout], [Skip], or lists of those. These
+/// annotations apply only on the given platforms. For example:
+///
+///     test('potentially slow test', () {
+///       // ...
+///     }, onPlatform: {
+///       // This test is especially slow on Windows.
+///       'windows': Timeout.factor(2),
+///       'browser': [
+///         Skip('TODO: add browser support'),
+///         // This will be slow on browsers once it works on them.
+///         Timeout.factor(2)
+///       ]
+///     });
+///
+/// If multiple platforms match, the annotations apply in order as through
+/// they were in nested groups.
+///
+/// If the `solo` flag is `true`, only tests and groups marked as
+/// "solo" will be be run. This only restricts tests *within this test
+/// suite*—tests in other suites will run as normal. We recommend that users
+/// avoid this flag if possible and instead use the test runner flag `-n` to
+/// filter tests by name.
+@isTest
+void test(description, dynamic Function() body,
+    {String? testOn,
+    Timeout? timeout,
+    skip,
+    tags,
+    Map<String, dynamic>? onPlatform,
+    int? retry,
+    @deprecated bool solo = false}) {
+  _declarer.test(description.toString(), body,
+      testOn: testOn,
+      timeout: timeout,
+      skip: skip,
+      onPlatform: onPlatform,
+      tags: tags,
+      retry: retry,
+      solo: solo);
+
+  // Force dart2js not to inline this function. We need it to be separate from
+  // `main()` in JS stack traces in order to properly determine the line and
+  // column where the test was defined. See sdk#26705.
+  return;
+  return; // ignore: dead_code
+}
+
+/// Creates a group of tests.
+///
+/// A group's description (converted to a string) is included in the descriptions
+/// of any tests or sub-groups it contains. [setUp] and [tearDown] are also scoped
+/// to the containing group.
+///
+/// If [testOn] is passed, it's parsed as a [platform selector][]; the test will
+/// only be run on matching platforms.
+///
+/// [platform selector]: https://github.com/dart-lang/test/tree/master/pkgs/test#platform-selectors
+///
+/// If [timeout] is passed, it's used to modify or replace the default timeout
+/// of 30 seconds. Timeout modifications take precedence in suite-group-test
+/// order, so [timeout] will also modify any timeouts set on the suite, and will
+/// be modified by any timeouts set on individual tests.
+///
+/// If [skip] is a String or `true`, the group is skipped. If it's a String, it
+/// should explain why the group is skipped; this reason will be printed instead
+/// of running the group's tests.
+///
+/// If [tags] is passed, it declares user-defined tags that are applied to the
+/// test. These tags can be used to select or skip the test on the command line,
+/// or to do bulk test configuration. All tags should be declared in the
+/// [package configuration file][configuring tags]. The parameter can be an
+/// [Iterable] of tag names, or a [String] representing a single tag.
+///
+/// [configuring tags]: https://github.com/dart-lang/test/blob/master/doc/package_config.md#configuring-tags
+///
+/// [onPlatform] allows groups to be configured on a platform-by-platform
+/// basis. It's a map from strings that are parsed as [PlatformSelector]s to
+/// annotation classes: [Timeout], [Skip], or lists of those. These
+/// annotations apply only on the given platforms. For example:
+///
+///     group('potentially slow tests', () {
+///       // ...
+///     }, onPlatform: {
+///       // These tests are especially slow on Windows.
+///       'windows': Timeout.factor(2),
+///       'browser': [
+///         Skip('TODO: add browser support'),
+///         // They'll be slow on browsers once it works on them.
+///         Timeout.factor(2)
+///       ]
+///     });
+///
+/// If multiple platforms match, the annotations apply in order as through
+/// they were in nested groups.
+///
+/// If the `solo` flag is `true`, only tests and groups marked as
+/// "solo" will be be run. This only restricts tests *within this test
+/// suite*—tests in other suites will run as normal. We recommend that users
+/// avoid this flag if possible, and instead use the test runner flag `-n` to
+/// filter tests by name.
+@isTestGroup
+void group(description, dynamic Function() body,
+    {String? testOn,
+    Timeout? timeout,
+    skip,
+    tags,
+    Map<String, dynamic>? onPlatform,
+    int? retry,
+    @deprecated bool solo = false}) {
+  _declarer.group(description.toString(), body,
+      testOn: testOn,
+      timeout: timeout,
+      skip: skip,
+      tags: tags,
+      onPlatform: onPlatform,
+      retry: retry,
+      solo: solo);
+
+  // Force dart2js not to inline this function. We need it to be separate from
+  // `main()` in JS stack traces in order to properly determine the line and
+  // column where the test was defined. See sdk#26705.
+  return;
+  return; // ignore: dead_code
+}
+
+/// Registers a function to be run before tests.
+///
+/// This function will be called before each test is run. [callback] may be
+/// asynchronous; if so, it must return a [Future].
+///
+/// If this is called within a test group, it applies only to tests in that
+/// group. [callback] will be run after any set-up callbacks in parent groups or
+/// at the top level.
+///
+/// Each callback at the top level or in a given group will be run in the order
+/// they were declared.
+void setUp(dynamic Function() callback) => _declarer.setUp(callback);
+
+/// Registers a function to be run after tests.
+///
+/// This function will be called after each test is run. [callback] may be
+/// asynchronous; if so, it must return a [Future].
+///
+/// If this is called within a test group, it applies only to tests in that
+/// group. [callback] will be run before any tear-down callbacks in parent
+/// groups or at the top level.
+///
+/// Each callback at the top level or in a given group will be run in the
+/// reverse of the order they were declared.
+///
+/// See also [addTearDown], which adds tear-downs to a running test.
+void tearDown(dynamic Function() callback) => _declarer.tearDown(callback);
+
+/// Registers a function to be run after the current test.
+///
+/// This is called within a running test, and adds a tear-down only for the
+/// current test. It allows testing libraries to add cleanup logic as soon as
+/// there's something to clean up.
+///
+/// The [callback] is run before any callbacks registered with [tearDown]. Like
+/// [tearDown], the most recently registered callback is run first.
+///
+/// If this is called from within a [setUpAll] or [tearDownAll] callback, it
+/// instead runs the function after *all* tests in the current test suite.
+void addTearDown(dynamic Function() callback) {
+  if (Invoker.current == null) {
+    throw StateError('addTearDown() may only be called within a test.');
+  }
+
+  Invoker.current!.addTearDown(callback);
+}
+
+/// Registers a function to be run once before all tests.
+///
+/// [callback] may be asynchronous; if so, it must return a [Future].
+///
+/// If this is called within a test group, [callback] will run before all tests
+/// in that group. It will be run after any [setUpAll] callbacks in parent
+/// groups or at the top level. It won't be run if none of the tests in the
+/// group are run.
+///
+/// **Note**: This function makes it very easy to accidentally introduce hidden
+/// dependencies between tests that should be isolated. In general, you should
+/// prefer [setUp], and only use [setUpAll] if the callback is prohibitively
+/// slow.
+void setUpAll(dynamic Function() callback) => _declarer.setUpAll(callback);
+
+/// Registers a function to be run once after all tests.
+///
+/// If this is called within a test group, [callback] will run after all tests
+/// in that group. It will be run before any [tearDownAll] callbacks in parent
+/// groups or at the top level. It won't be run if none of the tests in the
+/// group are run.
+///
+/// **Note**: This function makes it very easy to accidentally introduce hidden
+/// dependencies between tests that should be isolated. In general, you should
+/// prefer [tearDown], and only use [tearDownAll] if the callback is
+/// prohibitively slow.
+void tearDownAll(dynamic Function() callback) =>
+    _declarer.tearDownAll(callback);
diff --git a/pkgs/test_api/lib/src/frontend/timeout.dart b/pkgs/test_api/lib/src/scaffolding/timeout.dart
similarity index 100%
rename from pkgs/test_api/lib/src/frontend/timeout.dart
rename to pkgs/test_api/lib/src/scaffolding/timeout.dart
diff --git a/pkgs/test_api/lib/src/scaffolding/utils.dart b/pkgs/test_api/lib/src/scaffolding/utils.dart
new file mode 100644
index 0000000..1f2fa5d
--- /dev/null
+++ b/pkgs/test_api/lib/src/scaffolding/utils.dart
@@ -0,0 +1,43 @@
+// Copyright (c) 2021, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:async';
+
+import '../backend/invoker.dart';
+
+/// Returns a [Future] that completes after the [event loop][] has run the given
+/// number of [times] (20 by default).
+///
+/// [event loop]: https://medium.com/dartlang/dart-asynchronous-programming-isolates-and-event-loops-bffc3e296a6a
+///
+/// Awaiting this approximates waiting until all asynchronous work (other than
+/// work that's waiting for external resources) completes.
+Future pumpEventQueue({int times = 20}) {
+  if (times == 0) return Future.value();
+  // Use the event loop to allow the microtask queue to finish.
+  return Future(() => pumpEventQueue(times: times - 1));
+}
+
+/// Registers an exception that was caught for the current test.
+void registerException(Object error,
+    [StackTrace stackTrace = StackTrace.empty]) {
+  // This will usually forward directly to [Invoker.current.handleError], but
+  // going through the zone API allows other zones to consistently see errors.
+  Zone.current.handleUncaughtError(error, stackTrace);
+}
+
+/// Prints [message] if and when the current test fails.
+///
+/// This is intended for test infrastructure to provide debugging information
+/// without cluttering the output for successful tests. Note that unlike
+/// [print], each individual message passed to [printOnFailure] will be
+/// separated by a blank line.
+void printOnFailure(String message) => Invoker.current!.printOnFailure(message);
+
+/// Marks the current test as skipped.
+///
+/// A skipped test may still fail if any exception is thrown, including uncaught
+/// asynchronous errors. If the entire test should be skipped `return` from the
+/// test body after marking it as skipped.
+void markTestSkipped(String message) => Invoker.current!.skip(message);
diff --git a/pkgs/test_api/lib/src/util/pretty_print.dart b/pkgs/test_api/lib/src/util/pretty_print.dart
index 621f1f6..5c011c5 100644
--- a/pkgs/test_api/lib/src/util/pretty_print.dart
+++ b/pkgs/test_api/lib/src/util/pretty_print.dart
@@ -2,9 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'package:matcher/matcher.dart';
-import 'package:term_glyph/term_glyph.dart' as glyph;
-
 /// Returns [name] if [number] is 1, or the plural of [name] otherwise.
 ///
 /// By default, this just adds "s" to the end of [name] to get the plural. If
@@ -15,37 +12,6 @@
   return '${name}s';
 }
 
-/// Indent each line in [string] by [first.length] spaces.
-///
-/// [first] is used in place of the first line's indentation.
-String indent(String text, {required String first}) {
-  final prefix = ' ' * first.length;
-  var lines = text.split('\n');
-  if (lines.length == 1) return '$first$text';
-
-  var buffer = StringBuffer('$first${lines.first}\n');
-
-  // Write out all but the first and last lines with [prefix].
-  for (var line in lines.skip(1).take(lines.length - 2)) {
-    buffer.writeln('$prefix$line');
-  }
-  buffer.write('$prefix${lines.last}');
-  return buffer.toString();
-}
-
-/// Indents [text], and adds a bullet at the beginning.
-String addBullet(String text) => indent(text, first: '${glyph.bullet} ');
-
-/// Converts [strings] to a bulleted list.
-String bullet(Iterable<String> strings) => strings.map(addBullet).join('\n');
-
-/// Returns a pretty-printed representation of [value].
-///
-/// The matcher package doesn't expose its pretty-print function directly, but
-/// we can use it through StringDescription.
-String prettyPrint(value) =>
-    StringDescription().addDescriptionOf(value).toString();
-
 /// Returns a sentence fragment listing the elements of [iter].
 ///
 /// This converts each element of [iter] to a string and separates them with
diff --git a/pkgs/test_api/lib/src/util/remote_exception.dart b/pkgs/test_api/lib/src/util/remote_exception.dart
index 8f2e45a..a38104e 100644
--- a/pkgs/test_api/lib/src/util/remote_exception.dart
+++ b/pkgs/test_api/lib/src/util/remote_exception.dart
@@ -6,7 +6,7 @@
 
 import 'package:stack_trace/stack_trace.dart';
 
-import '../frontend/expect.dart';
+import '../../hooks.dart' show TestFailure;
 
 /// An exception that was thrown remotely.
 ///
diff --git a/pkgs/test_api/lib/test_api.dart b/pkgs/test_api/lib/test_api.dart
index 7ab4b13..3ee5866 100644
--- a/pkgs/test_api/lib/test_api.dart
+++ b/pkgs/test_api/lib/test_api.dart
@@ -6,291 +6,12 @@
     'Please use package:test.')
 library test_api;
 
-import 'dart:async';
-
-import 'package:meta/meta.dart';
-
-import 'src/backend/declarer.dart';
-import 'src/backend/invoker.dart';
-import 'src/frontend/timeout.dart';
-
-export 'package:matcher/matcher.dart';
-
-export 'src/frontend/expect.dart' hide formatFailure;
-export 'src/frontend/expect_async.dart';
-export 'src/frontend/future_matchers.dart';
-export 'src/frontend/never_called.dart';
-export 'src/frontend/on_platform.dart';
-export 'src/frontend/prints_matcher.dart';
-export 'src/frontend/retry.dart';
-export 'src/frontend/skip.dart';
-export 'src/frontend/spawn_hybrid.dart';
-export 'src/frontend/stream_matcher.dart';
-export 'src/frontend/stream_matchers.dart';
-export 'src/frontend/tags.dart';
-export 'src/frontend/test_on.dart';
-export 'src/frontend/throws_matcher.dart';
-export 'src/frontend/throws_matchers.dart';
-export 'src/frontend/timeout.dart';
-export 'src/frontend/utils.dart';
-
-// test_core does not support running tests directly, so the Declarer should
-// always be on the Zone.
-Declarer get _declarer => Zone.current[#test.declarer] as Declarer;
-
-// TODO(nweiz): This and other top-level functions should throw exceptions if
-// they're called after the declarer has finished declaring.
-/// Creates a new test case with the given description (converted to a string)
-/// and body.
-///
-/// The description will be added to the descriptions of any surrounding
-/// [group]s. If [testOn] is passed, it's parsed as a [platform selector][]; the
-/// test will only be run on matching platforms.
-///
-/// [platform selector]: https://github.com/dart-lang/test/tree/master/pkgs/test#platform-selectors
-///
-/// If [timeout] is passed, it's used to modify or replace the default timeout
-/// of 30 seconds. Timeout modifications take precedence in suite-group-test
-/// order, so [timeout] will also modify any timeouts set on the group or suite.
-///
-/// If [skip] is a String or `true`, the test is skipped. If it's a String, it
-/// should explain why the test is skipped; this reason will be printed instead
-/// of running the test.
-///
-/// If [tags] is passed, it declares user-defined tags that are applied to the
-/// test. These tags can be used to select or skip the test on the command line,
-/// or to do bulk test configuration. All tags should be declared in the
-/// [package configuration file][configuring tags]. The parameter can be an
-/// [Iterable] of tag names, or a [String] representing a single tag.
-///
-/// If [retry] is passed, the test will be retried the provided number of times
-/// before being marked as a failure.
-///
-/// [configuring tags]: https://github.com/dart-lang/test/blob/master/pkgs/test/doc/configuration.md#configuring-tags
-///
-/// [onPlatform] allows tests to be configured on a platform-by-platform
-/// basis. It's a map from strings that are parsed as [PlatformSelector]s to
-/// annotation classes: [Timeout], [Skip], or lists of those. These
-/// annotations apply only on the given platforms. For example:
-///
-///     test('potentially slow test', () {
-///       // ...
-///     }, onPlatform: {
-///       // This test is especially slow on Windows.
-///       'windows': Timeout.factor(2),
-///       'browser': [
-///         Skip('TODO: add browser support'),
-///         // This will be slow on browsers once it works on them.
-///         Timeout.factor(2)
-///       ]
-///     });
-///
-/// If multiple platforms match, the annotations apply in order as through
-/// they were in nested groups.
-///
-/// If the `solo` flag is `true`, only tests and groups marked as
-/// "solo" will be be run. This only restricts tests *within this test
-/// suite*—tests in other suites will run as normal. We recommend that users
-/// avoid this flag if possible and instead use the test runner flag `-n` to
-/// filter tests by name.
-@isTest
-void test(description, dynamic Function() body,
-    {String? testOn,
-    Timeout? timeout,
-    skip,
-    tags,
-    Map<String, dynamic>? onPlatform,
-    int? retry,
-    @deprecated bool solo = false}) {
-  _declarer.test(description.toString(), body,
-      testOn: testOn,
-      timeout: timeout,
-      skip: skip,
-      onPlatform: onPlatform,
-      tags: tags,
-      retry: retry,
-      solo: solo);
-
-  // Force dart2js not to inline this function. We need it to be separate from
-  // `main()` in JS stack traces in order to properly determine the line and
-  // column where the test was defined. See sdk#26705.
-  return;
-  return; // ignore: dead_code
-}
-
-/// Creates a group of tests.
-///
-/// A group's description (converted to a string) is included in the descriptions
-/// of any tests or sub-groups it contains. [setUp] and [tearDown] are also scoped
-/// to the containing group.
-///
-/// If [testOn] is passed, it's parsed as a [platform selector][]; the test will
-/// only be run on matching platforms.
-///
-/// [platform selector]: https://github.com/dart-lang/test/tree/master/pkgs/test#platform-selectors
-///
-/// If [timeout] is passed, it's used to modify or replace the default timeout
-/// of 30 seconds. Timeout modifications take precedence in suite-group-test
-/// order, so [timeout] will also modify any timeouts set on the suite, and will
-/// be modified by any timeouts set on individual tests.
-///
-/// If [skip] is a String or `true`, the group is skipped. If it's a String, it
-/// should explain why the group is skipped; this reason will be printed instead
-/// of running the group's tests.
-///
-/// If [tags] is passed, it declares user-defined tags that are applied to the
-/// test. These tags can be used to select or skip the test on the command line,
-/// or to do bulk test configuration. All tags should be declared in the
-/// [package configuration file][configuring tags]. The parameter can be an
-/// [Iterable] of tag names, or a [String] representing a single tag.
-///
-/// [configuring tags]: https://github.com/dart-lang/test/blob/master/doc/package_config.md#configuring-tags
-///
-/// [onPlatform] allows groups to be configured on a platform-by-platform
-/// basis. It's a map from strings that are parsed as [PlatformSelector]s to
-/// annotation classes: [Timeout], [Skip], or lists of those. These
-/// annotations apply only on the given platforms. For example:
-///
-///     group('potentially slow tests', () {
-///       // ...
-///     }, onPlatform: {
-///       // These tests are especially slow on Windows.
-///       'windows': Timeout.factor(2),
-///       'browser': [
-///         Skip('TODO: add browser support'),
-///         // They'll be slow on browsers once it works on them.
-///         Timeout.factor(2)
-///       ]
-///     });
-///
-/// If multiple platforms match, the annotations apply in order as through
-/// they were in nested groups.
-///
-/// If the `solo` flag is `true`, only tests and groups marked as
-/// "solo" will be be run. This only restricts tests *within this test
-/// suite*—tests in other suites will run as normal. We recommend that users
-/// avoid this flag if possible, and instead use the test runner flag `-n` to
-/// filter tests by name.
-@isTestGroup
-void group(description, dynamic Function() body,
-    {String? testOn,
-    Timeout? timeout,
-    skip,
-    tags,
-    Map<String, dynamic>? onPlatform,
-    int? retry,
-    @deprecated bool solo = false}) {
-  _declarer.group(description.toString(), body,
-      testOn: testOn,
-      timeout: timeout,
-      skip: skip,
-      tags: tags,
-      onPlatform: onPlatform,
-      retry: retry,
-      solo: solo);
-
-  // Force dart2js not to inline this function. We need it to be separate from
-  // `main()` in JS stack traces in order to properly determine the line and
-  // column where the test was defined. See sdk#26705.
-  return;
-  return; // ignore: dead_code
-}
-
-/// Registers a function to be run before tests.
-///
-/// This function will be called before each test is run. [callback] may be
-/// asynchronous; if so, it must return a [Future].
-///
-/// If this is called within a test group, it applies only to tests in that
-/// group. [callback] will be run after any set-up callbacks in parent groups or
-/// at the top level.
-///
-/// Each callback at the top level or in a given group will be run in the order
-/// they were declared.
-void setUp(dynamic Function() callback) => _declarer.setUp(callback);
-
-/// Registers a function to be run after tests.
-///
-/// This function will be called after each test is run. [callback] may be
-/// asynchronous; if so, it must return a [Future].
-///
-/// If this is called within a test group, it applies only to tests in that
-/// group. [callback] will be run before any tear-down callbacks in parent
-/// groups or at the top level.
-///
-/// Each callback at the top level or in a given group will be run in the
-/// reverse of the order they were declared.
-///
-/// See also [addTearDown], which adds tear-downs to a running test.
-void tearDown(dynamic Function() callback) => _declarer.tearDown(callback);
-
-/// Registers a function to be run after the current test.
-///
-/// This is called within a running test, and adds a tear-down only for the
-/// current test. It allows testing libraries to add cleanup logic as soon as
-/// there's something to clean up.
-///
-/// The [callback] is run before any callbacks registered with [tearDown]. Like
-/// [tearDown], the most recently registered callback is run first.
-///
-/// If this is called from within a [setUpAll] or [tearDownAll] callback, it
-/// instead runs the function after *all* tests in the current test suite.
-void addTearDown(dynamic Function() callback) {
-  if (Invoker.current == null) {
-    throw StateError('addTearDown() may only be called within a test.');
-  }
-
-  Invoker.current!.addTearDown(callback);
-}
-
-/// Registers a function to be run once before all tests.
-///
-/// [callback] may be asynchronous; if so, it must return a [Future].
-///
-/// If this is called within a test group, [callback] will run before all tests
-/// in that group. It will be run after any [setUpAll] callbacks in parent
-/// groups or at the top level. It won't be run if none of the tests in the
-/// group are run.
-///
-/// **Note**: This function makes it very easy to accidentally introduce hidden
-/// dependencies between tests that should be isolated. In general, you should
-/// prefer [setUp], and only use [setUpAll] if the callback is prohibitively
-/// slow.
-void setUpAll(dynamic Function() callback) => _declarer.setUpAll(callback);
-
-/// Registers a function to be run once after all tests.
-///
-/// If this is called within a test group, [callback] will run after all tests
-/// in that group. It will be run before any [tearDownAll] callbacks in parent
-/// groups or at the top level. It won't be run if none of the tests in the
-/// group are run.
-///
-/// **Note**: This function makes it very easy to accidentally introduce hidden
-/// dependencies between tests that should be isolated. In general, you should
-/// prefer [tearDown], and only use [tearDownAll] if the callback is
-/// prohibitively slow.
-void tearDownAll(dynamic Function() callback) =>
-    _declarer.tearDownAll(callback);
-
-/// Registers an exception that was caught for the current test.
-void registerException(Object error,
-    [StackTrace stackTrace = StackTrace.empty]) {
-  // This will usually forward directly to [Invoker.current.handleError], but
-  // going through the zone API allows other zones to consistently see errors.
-  Zone.current.handleUncaughtError(error, stackTrace);
-}
-
-/// Prints [message] if and when the current test fails.
-///
-/// This is intended for test infrastructure to provide debugging information
-/// without cluttering the output for successful tests. Note that unlike
-/// [print], each individual message passed to [printOnFailure] will be
-/// separated by a blank line.
-void printOnFailure(String message) => Invoker.current!.printOnFailure(message);
-
-/// Marks the current test as skipped.
-///
-/// A skipped test may still fail if any exception is thrown, including uncaught
-/// asynchronous errors. If the entire test should be skipped `return` from the
-/// test body after marking it as skipped.
-void markTestSkipped(String message) => Invoker.current!.skip(message);
+export 'expect.dart';
+export 'hooks.dart' show TestFailure;
+export 'scaffolding.dart';
+// Not yet deprecated, but not exposed through focused libraries.
+export 'src/scaffolding/utils.dart' show registerException;
+// Deprecated exports not surfaced through focused libraries.
+export 'src/expect/expect.dart' show ErrorFormatter;
+export 'src/expect/expect_async.dart' show expectAsync;
+export 'src/expect/throws_matcher.dart' show throws, Throws;
diff --git a/pkgs/test_api/test/backend/declarer_test.dart b/pkgs/test_api/test/backend/declarer_test.dart
index 69531d7..8426857 100644
--- a/pkgs/test_api/test/backend/declarer_test.dart
+++ b/pkgs/test_api/test/backend/declarer_test.dart
@@ -4,12 +4,11 @@
 
 import 'dart:async';
 
+import 'package:test/test.dart';
 import 'package:test_api/src/backend/group.dart';
 import 'package:test_api/src/backend/invoker.dart';
 import 'package:test_api/src/backend/suite.dart';
 import 'package:test_api/src/backend/test.dart';
-import 'package:test_api/src/frontend/timeout.dart';
-import 'package:test/test.dart';
 
 import '../utils.dart';
 
diff --git a/pkgs/test_api/test/backend/metadata_test.dart b/pkgs/test_api/test/backend/metadata_test.dart
index 44f1784..5a099df 100644
--- a/pkgs/test_api/test/backend/metadata_test.dart
+++ b/pkgs/test_api/test/backend/metadata_test.dart
@@ -8,8 +8,6 @@
 import 'package:test_api/src/backend/platform_selector.dart';
 import 'package:test_api/src/backend/runtime.dart';
 import 'package:test_api/src/backend/suite_platform.dart';
-import 'package:test_api/src/frontend/skip.dart';
-import 'package:test_api/src/frontend/timeout.dart';
 import 'package:test/test.dart';
 
 void main() {
diff --git a/pkgs/test_api/test/frontend/expect_async_test.dart b/pkgs/test_api/test/frontend/expect_async_test.dart
index 539ce2d..fb68246 100644
--- a/pkgs/test_api/test/frontend/expect_async_test.dart
+++ b/pkgs/test_api/test/frontend/expect_async_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+import 'dart:async';
+
 import 'package:test_api/src/backend/live_test.dart';
 import 'package:test_api/src/backend/state.dart';
 import 'package:test/test.dart';
@@ -306,6 +308,14 @@
     expectTestPassed(liveTest);
   });
 
+  test('may be called in a non-test zone', () async {
+    var liveTest = await runTestBody(() {
+      var callback = expectAsync0(() {});
+      Zone.root.run(callback);
+    });
+    expectTestPassed(liveTest);
+  });
+
   group('old-style expectAsync()', () {
     test('works with no arguments', () async {
       var callbackRun = false;
diff --git a/pkgs/test_core/CHANGELOG.md b/pkgs/test_core/CHANGELOG.md
index 3602465..e733f23 100644
--- a/pkgs/test_core/CHANGELOG.md
+++ b/pkgs/test_core/CHANGELOG.md
@@ -1,5 +1,7 @@
 ## 0.3.20-dev
 
+* Add library `scaffolding.dart` to allow importing a subset of the normal
+  surface area.
 * Remove `suiteChannel`. This is now handled by an additional argument to the
   `beforeLoad` callback in `serializeSuite`.
 * Disable stack trace chaining by default.
diff --git a/pkgs/test_core/lib/scaffolding.dart b/pkgs/test_core/lib/scaffolding.dart
new file mode 100644
index 0000000..ec4dd03
--- /dev/null
+++ b/pkgs/test_core/lib/scaffolding.dart
@@ -0,0 +1,290 @@
+// Copyright (c) 2021, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+@Deprecated('package:test_core is not intended for general use. '
+    'Please use package:test.')
+library test_core.scaffolding;
+
+import 'dart:async';
+
+import 'package:meta/meta.dart' show isTest, isTestGroup;
+import 'package:path/path.dart' as p;
+import 'package:test_api/backend.dart'; //ignore: deprecated_member_use
+import 'package:test_api/scaffolding.dart' show Timeout, pumpEventQueue;
+import 'package:test_api/src/backend/declarer.dart'; // ignore: implementation_imports
+import 'package:test_api/src/backend/invoker.dart'; // ignore: implementation_imports
+
+import 'src/runner/engine.dart';
+import 'src/runner/plugin/environment.dart';
+import 'src/runner/reporter/expanded.dart';
+import 'src/runner/runner_suite.dart';
+import 'src/runner/suite.dart';
+import 'src/util/async.dart';
+import 'src/util/os.dart';
+import 'src/util/print_sink.dart';
+
+// Hide implementations which don't support being run directly.
+// This file is an almost direct copy of import below, but with the global
+// declarer added.
+export 'package:test_api/scaffolding.dart'
+    hide test, group, setUp, setUpAll, tearDown, tearDownAll;
+
+/// The global declarer.
+///
+/// This is used if a test file is run directly, rather than through the runner.
+Declarer? _globalDeclarer;
+
+/// Gets the declarer for the current scope.
+///
+/// When using the runner, this returns the [Zone]-scoped declarer that's set by
+/// [IsolateListener] or [IframeListener]. If the test file is run directly,
+/// this returns [_globalDeclarer] (and sets it up on the first call).
+Declarer get _declarer {
+  var declarer = Declarer.current;
+  if (declarer != null) return declarer;
+  if (_globalDeclarer != null) return _globalDeclarer!;
+
+  // Since there's no Zone-scoped declarer, the test file is being run directly.
+  // In order to run the tests, we set up our own Declarer via
+  // [_globalDeclarer], and pump the event queue as a best effort to wait for
+  // all tests to be defined before starting them.
+  _globalDeclarer = Declarer();
+
+  () async {
+    await pumpEventQueue();
+
+    var suite = RunnerSuite(const PluginEnvironment(), SuiteConfiguration.empty,
+        _globalDeclarer!.build(), SuitePlatform(Runtime.vm, os: currentOSGuess),
+        path: p.prettyUri(Uri.base));
+
+    var engine = Engine();
+    engine.suiteSink.add(suite);
+    engine.suiteSink.close();
+    ExpandedReporter.watch(engine, PrintSink(),
+        color: true, printPath: false, printPlatform: false);
+
+    var success = await runZoned(() => Invoker.guard(engine.run),
+        zoneValues: {#test.declarer: _globalDeclarer});
+    if (success == true) return null;
+    print('');
+    unawaited(Future.error('Dummy exception to set exit code.'));
+  }();
+
+  return _globalDeclarer!;
+}
+
+// TODO(nweiz): This and other top-level functions should throw exceptions if
+// they're called after the declarer has finished declaring.
+/// Creates a new test case with the given description (converted to a string)
+/// and body.
+///
+/// The description will be added to the descriptions of any surrounding
+/// [group]s. If [testOn] is passed, it's parsed as a [platform selector][]; the
+/// test will only be run on matching platforms.
+///
+/// [platform selector]: https://github.com/dart-lang/test/tree/master/pkgs/test#platform-selectors
+///
+/// If [timeout] is passed, it's used to modify or replace the default timeout
+/// of 30 seconds. Timeout modifications take precedence in suite-group-test
+/// order, so [timeout] will also modify any timeouts set on the group or suite.
+///
+/// If [skip] is a String or `true`, the test is skipped. If it's a String, it
+/// should explain why the test is skipped; this reason will be printed instead
+/// of running the test.
+///
+/// If [tags] is passed, it declares user-defined tags that are applied to the
+/// test. These tags can be used to select or skip the test on the command line,
+/// or to do bulk test configuration. All tags should be declared in the
+/// [package configuration file][configuring tags]. The parameter can be an
+/// [Iterable] of tag names, or a [String] representing a single tag.
+///
+/// If [retry] is passed, the test will be retried the provided number of times
+/// before being marked as a failure.
+///
+/// [configuring tags]: https://github.com/dart-lang/test/blob/master/doc/package_config.md#configuring-tags
+///
+/// [onPlatform] allows tests to be configured on a platform-by-platform
+/// basis. It's a map from strings that are parsed as [PlatformSelector]s to
+/// annotation classes: [Timeout], [Skip], or lists of those. These
+/// annotations apply only on the given platforms. For example:
+///
+///     test('potentially slow test', () {
+///       // ...
+///     }, onPlatform: {
+///       // This test is especially slow on Windows.
+///       'windows': Timeout.factor(2),
+///       'browser': [
+///         Skip('TODO: add browser support'),
+///         // This will be slow on browsers once it works on them.
+///         Timeout.factor(2)
+///       ]
+///     });
+///
+/// If multiple platforms match, the annotations apply in order as through
+/// they were in nested groups.
+///
+/// If the `solo` flag is `true`, only tests and groups marked as
+/// "solo" will be be run. This only restricts tests *within this test
+/// suite*—tests in other suites will run as normal. We recommend that users
+/// avoid this flag if possible and instead use the test runner flag `-n` to
+/// filter tests by name.
+@isTest
+void test(description, dynamic Function() body,
+    {String? testOn,
+    Timeout? timeout,
+    skip,
+    tags,
+    Map<String, dynamic>? onPlatform,
+    int? retry,
+    @deprecated bool solo = false}) {
+  _declarer.test(description.toString(), body,
+      testOn: testOn,
+      timeout: timeout,
+      skip: skip,
+      onPlatform: onPlatform,
+      tags: tags,
+      retry: retry,
+      solo: solo);
+
+  // Force dart2js not to inline this function. We need it to be separate from
+  // `main()` in JS stack traces in order to properly determine the line and
+  // column where the test was defined. See sdk#26705.
+  return;
+  return; // ignore: dead_code
+}
+
+/// Creates a group of tests.
+///
+/// A group's description (converted to a string) is included in the descriptions
+/// of any tests or sub-groups it contains. [setUp] and [tearDown] are also scoped
+/// to the containing group.
+///
+/// If [testOn] is passed, it's parsed as a [platform selector][]; the test will
+/// only be run on matching platforms.
+///
+/// [platform selector]: https://github.com/dart-lang/test/tree/master/pkgs/test#platform-selectors
+///
+/// If [timeout] is passed, it's used to modify or replace the default timeout
+/// of 30 seconds. Timeout modifications take precedence in suite-group-test
+/// order, so [timeout] will also modify any timeouts set on the suite, and will
+/// be modified by any timeouts set on individual tests.
+///
+/// If [skip] is a String or `true`, the group is skipped. If it's a String, it
+/// should explain why the group is skipped; this reason will be printed instead
+/// of running the group's tests.
+///
+/// If [tags] is passed, it declares user-defined tags that are applied to the
+/// test. These tags can be used to select or skip the test on the command line,
+/// or to do bulk test configuration. All tags should be declared in the
+/// [package configuration file][configuring tags]. The parameter can be an
+/// [Iterable] of tag names, or a [String] representing a single tag.
+///
+/// [configuring tags]: https://github.com/dart-lang/test/blob/master/doc/package_config.md#configuring-tags
+///
+/// [onPlatform] allows groups to be configured on a platform-by-platform
+/// basis. It's a map from strings that are parsed as [PlatformSelector]s to
+/// annotation classes: [Timeout], [Skip], or lists of those. These
+/// annotations apply only on the given platforms. For example:
+///
+///     group('potentially slow tests', () {
+///       // ...
+///     }, onPlatform: {
+///       // These tests are especially slow on Windows.
+///       'windows': Timeout.factor(2),
+///       'browser': [
+///         Skip('TODO: add browser support'),
+///         // They'll be slow on browsers once it works on them.
+///         Timeout.factor(2)
+///       ]
+///     });
+///
+/// If multiple platforms match, the annotations apply in order as through
+/// they were in nested groups.
+///
+/// If the `solo` flag is `true`, only tests and groups marked as
+/// "solo" will be be run. This only restricts tests *within this test
+/// suite*—tests in other suites will run as normal. We recommend that users
+/// avoid this flag if possible, and instead use the test runner flag `-n` to
+/// filter tests by name.
+@isTestGroup
+void group(description, dynamic Function() body,
+    {String? testOn,
+    Timeout? timeout,
+    skip,
+    tags,
+    Map<String, dynamic>? onPlatform,
+    int? retry,
+    @deprecated bool solo = false}) {
+  _declarer.group(description.toString(), body,
+      testOn: testOn,
+      timeout: timeout,
+      skip: skip,
+      tags: tags,
+      onPlatform: onPlatform,
+      retry: retry,
+      solo: solo);
+
+  // Force dart2js not to inline this function. We need it to be separate from
+  // `main()` in JS stack traces in order to properly determine the line and
+  // column where the test was defined. See sdk#26705.
+  return;
+  return; // ignore: dead_code
+}
+
+/// Registers a function to be run before tests.
+///
+/// This function will be called before each test is run. [callback] may be
+/// asynchronous; if so, it must return a [Future].
+///
+/// If this is called within a test group, it applies only to tests in that
+/// group. [callback] will be run after any set-up callbacks in parent groups or
+/// at the top level.
+///
+/// Each callback at the top level or in a given group will be run in the order
+/// they were declared.
+void setUp(dynamic Function() callback) => _declarer.setUp(callback);
+
+/// Registers a function to be run after tests.
+///
+/// This function will be called after each test is run. [callback] may be
+/// asynchronous; if so, it must return a [Future].
+///
+/// If this is called within a test group, it applies only to tests in that
+/// group. [callback] will be run before any tear-down callbacks in parent
+/// groups or at the top level.
+///
+/// Each callback at the top level or in a given group will be run in the
+/// reverse of the order they were declared.
+///
+/// See also [addTearDown], which adds tear-downs to a running test.
+void tearDown(dynamic Function() callback) => _declarer.tearDown(callback);
+
+/// Registers a function to be run once before all tests.
+///
+/// [callback] may be asynchronous; if so, it must return a [Future].
+///
+/// If this is called within a test group, [callback] will run before all tests
+/// in that group. It will be run after any [setUpAll] callbacks in parent
+/// groups or at the top level. It won't be run if none of the tests in the
+/// group are run.
+///
+/// **Note**: This function makes it very easy to accidentally introduce hidden
+/// dependencies between tests that should be isolated. In general, you should
+/// prefer [setUp], and only use [setUpAll] if the callback is prohibitively
+/// slow.
+void setUpAll(dynamic Function() callback) => _declarer.setUpAll(callback);
+
+/// Registers a function to be run once after all tests.
+///
+/// If this is called within a test group, [callback] will run after all tests
+/// in that group. It will be run before any [tearDownAll] callbacks in parent
+/// groups or at the top level. It won't be run if none of the tests in the
+/// group are run.
+///
+/// **Note**: This function makes it very easy to accidentally introduce hidden
+/// dependencies between tests that should be isolated. In general, you should
+/// prefer [tearDown], and only use [tearDownAll] if the callback is
+/// prohibitively slow.
+void tearDownAll(dynamic Function() callback) =>
+    _declarer.tearDownAll(callback);
diff --git a/pkgs/test_core/lib/src/runner/configuration.dart b/pkgs/test_core/lib/src/runner/configuration.dart
index 28874d6..cdf1f75 100644
--- a/pkgs/test_core/lib/src/runner/configuration.dart
+++ b/pkgs/test_core/lib/src/runner/configuration.dart
@@ -9,10 +9,11 @@
 import 'package:glob/glob.dart';
 import 'package:path/path.dart' as p;
 import 'package:source_span/source_span.dart';
-
+import 'package:test_api/scaffolding.dart' // ignore: deprecated_member_use
+    show
+        Timeout;
 import 'package:test_api/src/backend/platform_selector.dart'; // ignore: implementation_imports
 import 'package:test_api/src/backend/runtime.dart'; // ignore: implementation_imports
-import 'package:test_api/src/frontend/timeout.dart'; // ignore: implementation_imports
 
 import '../util/io.dart';
 import 'configuration/args.dart' as args;
diff --git a/pkgs/test_core/lib/src/runner/configuration/args.dart b/pkgs/test_core/lib/src/runner/configuration/args.dart
index c1ff9fb..efdc2ae 100644
--- a/pkgs/test_core/lib/src/runner/configuration/args.dart
+++ b/pkgs/test_core/lib/src/runner/configuration/args.dart
@@ -7,8 +7,10 @@
 
 import 'package:args/args.dart';
 import 'package:boolean_selector/boolean_selector.dart';
+import 'package:test_api/scaffolding.dart' // ignore: deprecated_member_use
+    show
+        Timeout;
 import 'package:test_api/src/backend/runtime.dart'; // ignore: implementation_imports
-import 'package:test_api/src/frontend/timeout.dart'; // ignore: implementation_imports
 
 import '../../util/io.dart';
 import '../configuration.dart';
diff --git a/pkgs/test_core/lib/src/runner/configuration/load.dart b/pkgs/test_core/lib/src/runner/configuration/load.dart
index 7a5116a..9a23915 100644
--- a/pkgs/test_core/lib/src/runner/configuration/load.dart
+++ b/pkgs/test_core/lib/src/runner/configuration/load.dart
@@ -9,9 +9,11 @@
 import 'package:meta/meta.dart';
 import 'package:path/path.dart' as p;
 import 'package:source_span/source_span.dart';
+import 'package:test_api/scaffolding.dart' // ignore: deprecated_member_use
+    show
+        Timeout;
 import 'package:test_api/src/backend/operating_system.dart'; // ignore: implementation_imports
 import 'package:test_api/src/backend/platform_selector.dart'; // ignore: implementation_imports
-import 'package:test_api/src/frontend/timeout.dart'; // ignore: implementation_imports
 import 'package:test_api/src/utils.dart'; // ignore: implementation_imports
 import 'package:yaml/yaml.dart';
 
diff --git a/pkgs/test_core/lib/src/runner/parse_metadata.dart b/pkgs/test_core/lib/src/runner/parse_metadata.dart
index 4576d76..a68422b 100644
--- a/pkgs/test_core/lib/src/runner/parse_metadata.dart
+++ b/pkgs/test_core/lib/src/runner/parse_metadata.dart
@@ -6,9 +6,11 @@
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:path/path.dart' as p;
 import 'package:source_span/source_span.dart';
+import 'package:test_api/scaffolding.dart' // ignore: deprecated_member_use
+    show
+        Timeout;
 import 'package:test_api/src/backend/metadata.dart'; // ignore: implementation_imports
 import 'package:test_api/src/backend/platform_selector.dart'; // ignore: implementation_imports
-import 'package:test_api/src/frontend/timeout.dart'; // ignore: implementation_imports
 import 'package:test_api/src/utils.dart'; // ignore: implementation_imports
 
 import '../util/dart.dart';
diff --git a/pkgs/test_core/lib/src/runner/reporter/json.dart b/pkgs/test_core/lib/src/runner/reporter/json.dart
index 4be3734..c16c420 100644
--- a/pkgs/test_core/lib/src/runner/reporter/json.dart
+++ b/pkgs/test_core/lib/src/runner/reporter/json.dart
@@ -15,7 +15,9 @@
 import 'package:test_api/src/backend/runtime.dart'; // ignore: implementation_imports
 import 'package:test_api/src/backend/state.dart'; // ignore: implementation_imports
 import 'package:test_api/src/backend/suite.dart'; // ignore: implementation_imports
-import 'package:test_api/src/frontend/expect.dart'; // ignore: implementation_imports
+import 'package:test_api/hooks.dart' // ignore: implementation_imports
+    show
+        TestFailure;
 
 import '../configuration.dart';
 import '../engine.dart';
diff --git a/pkgs/test_core/lib/src/runner/suite.dart b/pkgs/test_core/lib/src/runner/suite.dart
index b656041..2cd1e07 100644
--- a/pkgs/test_core/lib/src/runner/suite.dart
+++ b/pkgs/test_core/lib/src/runner/suite.dart
@@ -5,12 +5,13 @@
 import 'package:boolean_selector/boolean_selector.dart';
 import 'package:collection/collection.dart';
 import 'package:source_span/source_span.dart';
-
+import 'package:test_api/scaffolding.dart' // ignore: deprecated_member_use
+    show
+        Timeout;
 import 'package:test_api/src/backend/metadata.dart'; // ignore: implementation_imports
 import 'package:test_api/src/backend/platform_selector.dart'; // ignore: implementation_imports
-import 'package:test_api/src/backend/suite_platform.dart'; // ignore: implementation_imports
 import 'package:test_api/src/backend/runtime.dart'; // ignore: implementation_imports
-import 'package:test_api/src/frontend/timeout.dart'; // ignore: implementation_imports
+import 'package:test_api/src/backend/suite_platform.dart'; // ignore: implementation_imports
 
 import 'runtime_selection.dart';
 
diff --git a/pkgs/test_core/lib/test_core.dart b/pkgs/test_core/lib/test_core.dart
index f0f8625..428580a 100644
--- a/pkgs/test_core/lib/test_core.dart
+++ b/pkgs/test_core/lib/test_core.dart
@@ -6,288 +6,11 @@
     'Please use package:test.')
 library test_core;
 
-import 'dart:async';
-
-import 'package:meta/meta.dart' show isTest, isTestGroup;
-import 'package:path/path.dart' as p;
-import 'package:test_api/backend.dart'; //ignore: deprecated_member_use
-import 'package:test_api/src/backend/declarer.dart'; // ignore: implementation_imports
-import 'package:test_api/src/backend/invoker.dart'; // ignore: implementation_imports
-import 'package:test_api/src/frontend/timeout.dart'; // ignore: implementation_imports
-import 'package:test_api/src/frontend/utils.dart'; // ignore: implementation_imports
-
-import 'src/runner/engine.dart';
-import 'src/runner/plugin/environment.dart';
-import 'src/runner/reporter/expanded.dart';
-import 'src/runner/runner_suite.dart';
-import 'src/runner/suite.dart';
-import 'src/util/async.dart';
-import 'src/util/os.dart';
-import 'src/util/print_sink.dart';
-
-export 'package:matcher/matcher.dart';
-// Hide implementations which don't support being run directly.
-// This file is an almost direct copy of import below, but with the global
-// declarer added.
-//ignore: deprecated_member_use
+export 'scaffolding.dart';
+export 'package:test_api/expect.dart';
+export 'package:test_api/hooks.dart' show TestFailure;
+// Not yet deprecated, but not exposed through focused libraries.
+export 'package:test_api/test_api.dart' show registerException;
+// Deprecated exports not surfaced through focused libraries.
 export 'package:test_api/test_api.dart'
-    hide test, group, setUp, setUpAll, tearDown, tearDownAll;
-
-/// The global declarer.
-///
-/// This is used if a test file is run directly, rather than through the runner.
-Declarer? _globalDeclarer;
-
-/// Gets the declarer for the current scope.
-///
-/// When using the runner, this returns the [Zone]-scoped declarer that's set by
-/// [IsolateListener] or [IframeListener]. If the test file is run directly,
-/// this returns [_globalDeclarer] (and sets it up on the first call).
-Declarer get _declarer {
-  var declarer = Declarer.current;
-  if (declarer != null) return declarer;
-  if (_globalDeclarer != null) return _globalDeclarer!;
-
-  // Since there's no Zone-scoped declarer, the test file is being run directly.
-  // In order to run the tests, we set up our own Declarer via
-  // [_globalDeclarer], and pump the event queue as a best effort to wait for
-  // all tests to be defined before starting them.
-  _globalDeclarer = Declarer();
-
-  () async {
-    await pumpEventQueue();
-
-    var suite = RunnerSuite(const PluginEnvironment(), SuiteConfiguration.empty,
-        _globalDeclarer!.build(), SuitePlatform(Runtime.vm, os: currentOSGuess),
-        path: p.prettyUri(Uri.base));
-
-    var engine = Engine();
-    engine.suiteSink.add(suite);
-    engine.suiteSink.close();
-    ExpandedReporter.watch(engine, PrintSink(),
-        color: true, printPath: false, printPlatform: false);
-
-    var success = await runZoned(() => Invoker.guard(engine.run),
-        zoneValues: {#test.declarer: _globalDeclarer});
-    if (success == true) return null;
-    print('');
-    unawaited(Future.error('Dummy exception to set exit code.'));
-  }();
-
-  return _globalDeclarer!;
-}
-
-// TODO(nweiz): This and other top-level functions should throw exceptions if
-// they're called after the declarer has finished declaring.
-/// Creates a new test case with the given description (converted to a string)
-/// and body.
-///
-/// The description will be added to the descriptions of any surrounding
-/// [group]s. If [testOn] is passed, it's parsed as a [platform selector][]; the
-/// test will only be run on matching platforms.
-///
-/// [platform selector]: https://github.com/dart-lang/test/tree/master/pkgs/test#platform-selectors
-///
-/// If [timeout] is passed, it's used to modify or replace the default timeout
-/// of 30 seconds. Timeout modifications take precedence in suite-group-test
-/// order, so [timeout] will also modify any timeouts set on the group or suite.
-///
-/// If [skip] is a String or `true`, the test is skipped. If it's a String, it
-/// should explain why the test is skipped; this reason will be printed instead
-/// of running the test.
-///
-/// If [tags] is passed, it declares user-defined tags that are applied to the
-/// test. These tags can be used to select or skip the test on the command line,
-/// or to do bulk test configuration. All tags should be declared in the
-/// [package configuration file][configuring tags]. The parameter can be an
-/// [Iterable] of tag names, or a [String] representing a single tag.
-///
-/// If [retry] is passed, the test will be retried the provided number of times
-/// before being marked as a failure.
-///
-/// [configuring tags]: https://github.com/dart-lang/test/blob/master/pkgs/test/doc/configuration.md#configuring-tags
-///
-/// [onPlatform] allows tests to be configured on a platform-by-platform
-/// basis. It's a map from strings that are parsed as [PlatformSelector]s to
-/// annotation classes: [Timeout], [Skip], or lists of those. These
-/// annotations apply only on the given platforms. For example:
-///
-///     test('potentially slow test', () {
-///       // ...
-///     }, onPlatform: {
-///       // This test is especially slow on Windows.
-///       'windows': Timeout.factor(2),
-///       'browser': [
-///         Skip('TODO: add browser support'),
-///         // This will be slow on browsers once it works on them.
-///         Timeout.factor(2)
-///       ]
-///     });
-///
-/// If multiple platforms match, the annotations apply in order as through
-/// they were in nested groups.
-///
-/// If the `solo` flag is `true`, only tests and groups marked as
-/// "solo" will be be run. This only restricts tests *within this test
-/// suite*—tests in other suites will run as normal. We recommend that users
-/// avoid this flag if possible and instead use the test runner flag `-n` to
-/// filter tests by name.
-@isTest
-void test(description, dynamic Function() body,
-    {String? testOn,
-    Timeout? timeout,
-    skip,
-    tags,
-    Map<String, dynamic>? onPlatform,
-    int? retry,
-    @deprecated bool solo = false}) {
-  _declarer.test(description.toString(), body,
-      testOn: testOn,
-      timeout: timeout,
-      skip: skip,
-      onPlatform: onPlatform,
-      tags: tags,
-      retry: retry,
-      solo: solo);
-
-  // Force dart2js not to inline this function. We need it to be separate from
-  // `main()` in JS stack traces in order to properly determine the line and
-  // column where the test was defined. See sdk#26705.
-  return;
-  return; // ignore: dead_code
-}
-
-/// Creates a group of tests.
-///
-/// A group's description (converted to a string) is included in the descriptions
-/// of any tests or sub-groups it contains. [setUp] and [tearDown] are also scoped
-/// to the containing group.
-///
-/// If [testOn] is passed, it's parsed as a [platform selector][]; the test will
-/// only be run on matching platforms.
-///
-/// [platform selector]: https://github.com/dart-lang/test/tree/master/pkgs/test#platform-selectors
-///
-/// If [timeout] is passed, it's used to modify or replace the default timeout
-/// of 30 seconds. Timeout modifications take precedence in suite-group-test
-/// order, so [timeout] will also modify any timeouts set on the suite, and will
-/// be modified by any timeouts set on individual tests.
-///
-/// If [skip] is a String or `true`, the group is skipped. If it's a String, it
-/// should explain why the group is skipped; this reason will be printed instead
-/// of running the group's tests.
-///
-/// If [tags] is passed, it declares user-defined tags that are applied to the
-/// test. These tags can be used to select or skip the test on the command line,
-/// or to do bulk test configuration. All tags should be declared in the
-/// [package configuration file][configuring tags]. The parameter can be an
-/// [Iterable] of tag names, or a [String] representing a single tag.
-///
-/// [configuring tags]: https://github.com/dart-lang/test/blob/master/pkgs/test/doc/configuration.md#configuring-tags
-///
-/// [onPlatform] allows groups to be configured on a platform-by-platform
-/// basis. It's a map from strings that are parsed as [PlatformSelector]s to
-/// annotation classes: [Timeout], [Skip], or lists of those. These
-/// annotations apply only on the given platforms. For example:
-///
-///     group('potentially slow tests', () {
-///       // ...
-///     }, onPlatform: {
-///       // These tests are especially slow on Windows.
-///       'windows': Timeout.factor(2),
-///       'browser': [
-///         Skip('TODO: add browser support'),
-///         // They'll be slow on browsers once it works on them.
-///         Timeout.factor(2)
-///       ]
-///     });
-///
-/// If multiple platforms match, the annotations apply in order as through
-/// they were in nested groups.
-///
-/// If the `solo` flag is `true`, only tests and groups marked as
-/// "solo" will be be run. This only restricts tests *within this test
-/// suite*—tests in other suites will run as normal. We recommend that users
-/// avoid this flag if possible, and instead use the test runner flag `-n` to
-/// filter tests by name.
-@isTestGroup
-void group(description, dynamic Function() body,
-    {String? testOn,
-    Timeout? timeout,
-    skip,
-    tags,
-    Map<String, dynamic>? onPlatform,
-    int? retry,
-    @deprecated bool solo = false}) {
-  _declarer.group(description.toString(), body,
-      testOn: testOn,
-      timeout: timeout,
-      skip: skip,
-      tags: tags,
-      onPlatform: onPlatform,
-      retry: retry,
-      solo: solo);
-
-  // Force dart2js not to inline this function. We need it to be separate from
-  // `main()` in JS stack traces in order to properly determine the line and
-  // column where the test was defined. See sdk#26705.
-  return;
-  return; // ignore: dead_code
-}
-
-/// Registers a function to be run before tests.
-///
-/// This function will be called before each test is run. [callback] may be
-/// asynchronous; if so, it must return a [Future].
-///
-/// If this is called within a test group, it applies only to tests in that
-/// group. [callback] will be run after any set-up callbacks in parent groups or
-/// at the top level.
-///
-/// Each callback at the top level or in a given group will be run in the order
-/// they were declared.
-void setUp(dynamic Function() callback) => _declarer.setUp(callback);
-
-/// Registers a function to be run after tests.
-///
-/// This function will be called after each test is run. [callback] may be
-/// asynchronous; if so, it must return a [Future].
-///
-/// If this is called within a test group, it applies only to tests in that
-/// group. [callback] will be run before any tear-down callbacks in parent
-/// groups or at the top level.
-///
-/// Each callback at the top level or in a given group will be run in the
-/// reverse of the order they were declared.
-///
-/// See also [addTearDown], which adds tear-downs to a running test.
-void tearDown(dynamic Function() callback) => _declarer.tearDown(callback);
-
-/// Registers a function to be run once before all tests.
-///
-/// [callback] may be asynchronous; if so, it must return a [Future].
-///
-/// If this is called within a test group, [callback] will run before all tests
-/// in that group. It will be run after any [setUpAll] callbacks in parent
-/// groups or at the top level. It won't be run if none of the tests in the
-/// group are run.
-///
-/// **Note**: This function makes it very easy to accidentally introduce hidden
-/// dependencies between tests that should be isolated. In general, you should
-/// prefer [setUp], and only use [setUpAll] if the callback is prohibitively
-/// slow.
-void setUpAll(dynamic Function() callback) => _declarer.setUpAll(callback);
-
-/// Registers a function to be run once after all tests.
-///
-/// If this is called within a test group, [callback] will run after all tests
-/// in that group. It will be run before any [tearDownAll] callbacks in parent
-/// groups or at the top level. It won't be run if none of the tests in the
-/// group are run.
-///
-/// **Note**: This function makes it very easy to accidentally introduce hidden
-/// dependencies between tests that should be isolated. In general, you should
-/// prefer [tearDown], and only use [tearDownAll] if the callback is
-/// prohibitively slow.
-void tearDownAll(dynamic Function() callback) =>
-    _declarer.tearDownAll(callback);
+    show ErrorFormatter, expectAsync, throws, Throws;