Add helpers to make it easier to do stuff in the sandbox (dart-lang/test_descriptor#13)

diff --git a/pkgs/test_descriptor/CHANGELOG.md b/pkgs/test_descriptor/CHANGELOG.md
index 81c5461..cbdb5cd 100644
--- a/pkgs/test_descriptor/CHANGELOG.md
+++ b/pkgs/test_descriptor/CHANGELOG.md

@@ -1,3 +1,11 @@
+## 1.1.0
+
+* Add a `path()` function that returns the a path within the sandbox directory.
+
+* Add `io` getters to `FileDescriptor` and `DirectoryDescriptor` that returns
+  `dart:io` `File` and `Directory` objects, respectively, within the sandbox
+  directory.
+
 ## 1.0.4
 
 * Support test `1.x.x'.

diff --git a/pkgs/test_descriptor/lib/src/directory_descriptor.dart b/pkgs/test_descriptor/lib/src/directory_descriptor.dart
index 32b2e07..0b9f36f 100644
--- a/pkgs/test_descriptor/lib/src/directory_descriptor.dart
+++ b/pkgs/test_descriptor/lib/src/directory_descriptor.dart

@@ -27,6 +27,10 @@
   /// This may be modified.
   final List<Descriptor> contents;
 
+  /// Returns a `dart:io` [Directory] object that refers to this file within
+  /// [sandbox].
+  Directory get io => new Directory(p.join(sandbox, name));
+
   DirectoryDescriptor(String name, Iterable<Descriptor> contents)
       : contents = contents.toList(),
         super(name);

diff --git a/pkgs/test_descriptor/lib/src/file_descriptor.dart b/pkgs/test_descriptor/lib/src/file_descriptor.dart
index 1d7a109..ef030f0 100644
--- a/pkgs/test_descriptor/lib/src/file_descriptor.dart
+++ b/pkgs/test_descriptor/lib/src/file_descriptor.dart

@@ -44,6 +44,10 @@
     return new _MatcherFileDescriptor(name, contents);
   }
 
+  /// Returns a `dart:io` [File] object that refers to this file within
+  /// [sandbox].
+  File get io => new File(p.join(sandbox, name));
+
   /// Creates a new binary [FileDescriptor] with [name] that matches its binary
   /// contents against [matcher].
   ///

diff --git a/pkgs/test_descriptor/lib/test_descriptor.dart b/pkgs/test_descriptor/lib/test_descriptor.dart
index 54649ab..fe27b92 100644
--- a/pkgs/test_descriptor/lib/test_descriptor.dart
+++ b/pkgs/test_descriptor/lib/test_descriptor.dart

@@ -2,6 +2,7 @@
 // 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:path/path.dart' as p;
 import 'package:test/test.dart';
 
 import 'src/descriptor.dart';
@@ -9,6 +10,7 @@
 import 'src/file_descriptor.dart';
 import 'src/nothing_descriptor.dart';
 import 'src/pattern_descriptor.dart';
+import 'src/sandbox.dart';
 
 export 'src/descriptor.dart';
 export 'src/directory_descriptor.dart';
@@ -70,3 +72,6 @@
 /// constructs a [DirectoryDescriptor] descriptor.
 PatternDescriptor dirPattern(Pattern name, [Iterable<Descriptor> contents]) =>
     pattern(name, (realName) => dir(realName, contents));
+
+/// Returns [path] within the [sandbox] directory.
+String path(String path) => p.join(sandbox, path);

diff --git a/pkgs/test_descriptor/pubspec.yaml b/pkgs/test_descriptor/pubspec.yaml
index c304171..af77fab 100644
--- a/pkgs/test_descriptor/pubspec.yaml
+++ b/pkgs/test_descriptor/pubspec.yaml

@@ -1,5 +1,5 @@
 name: test_descriptor
-version: 1.0.4
+version: 1.1.0
 description: An API for defining and verifying directory structures.
 author: Dart Team <misc@dartlang.org>
 homepage: https://github.com/dart-lang/test_descriptor

diff --git a/pkgs/test_descriptor/test/directory_test.dart b/pkgs/test_descriptor/test/directory_test.dart
index 5507ea4..97dcacb 100644
--- a/pkgs/test_descriptor/test/directory_test.dart
+++ b/pkgs/test_descriptor/test/directory_test.dart

@@ -300,4 +300,8 @@
       ]).validate();
     });
   });
+
+  test("io refers to the directory within the sandbox", () {
+    expect(d.file('dir').io.path, equals(p.join(d.sandbox, 'dir')));
+  });
 }

diff --git a/pkgs/test_descriptor/test/file_test.dart b/pkgs/test_descriptor/test/file_test.dart
index b3be840..70093c1 100644
--- a/pkgs/test_descriptor/test/file_test.dart
+++ b/pkgs/test_descriptor/test/file_test.dart

@@ -154,4 +154,8 @@
           throwsUnsupportedError);
     });
   });
+
+  test("io refers to the file within the sandbox", () {
+    expect(d.file('name.txt').io.path, equals(p.join(d.sandbox, 'name.txt')));
+  });
 }

diff --git a/pkgs/test_descriptor/test/sandbox_test.dart b/pkgs/test_descriptor/test/sandbox_test.dart
new file mode 100644
index 0000000..34c90ac
--- /dev/null
+++ b/pkgs/test_descriptor/test/sandbox_test.dart

@@ -0,0 +1,35 @@
+// Copyright (c) 2018, 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.
+
+@TestOn('vm')
+
+import 'dart:async';
+import 'dart:convert';
+import 'dart:io';
+
+import 'package:path/path.dart' as p;
+import 'package:test/test.dart';
+
+import 'package:test_descriptor/test_descriptor.dart' as d;
+
+import 'utils.dart';
+
+void main() {
+  test("accessing the getter creates the directory", () {
+    expect(new Directory(d.sandbox).existsSync(), isTrue);
+  });
+
+  test("the directory is deleted after the test", () {
+    String sandbox;
+    addTearDown(() {
+      expect(new Directory(sandbox).existsSync(), isFalse);
+    });
+
+    sandbox = d.sandbox;
+  });
+
+  test("path() returns a path in the sandbox", () {
+    expect(d.path("foo"), equals(p.join(d.sandbox, "foo")));
+  });
+}