[code_builder] Expand code coverage (#2409)

pkgs/code_builder/test/specs/function_type_test.dart

diff --git a/pkgs/code_builder/test/specs/function_type_test.dart b/pkgs/code_builder/test/specs/function_type_test.dart
new file mode 100644
index 0000000..2491a26
--- /dev/null
+++ b/pkgs/code_builder/test/specs/function_type_test.dart
@@ -0,0 +1,64 @@
+// Copyright (c) 2026, 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:code_builder/code_builder.dart';
+import 'package:test/test.dart';
+
+import '../common.dart';
+
+void main() {
+  late DartEmitter emitter;
+
+  useDartfmt();
+
+  setUp(() => emitter = DartEmitter.scoped(useNullSafetySyntax: true));
+
+  group('FunctionType API contracts', () {
+    test('properties should be correct', () {
+      final funcType = FunctionType();
+      expect(funcType.url, isNull);
+      expect(funcType.symbol, isNull);
+      expect(funcType.type, same(funcType));
+    });
+
+    test('newInstance should throw UnsupportedError', () {
+      final funcType = FunctionType();
+      expect(() => funcType.newInstance([]), throwsUnsupportedError);
+    });
+
+    test('newInstanceNamed should throw UnsupportedError', () {
+      final funcType = FunctionType();
+      expect(
+        () => funcType.newInstanceNamed('name', []),
+        throwsUnsupportedError,
+      );
+    });
+
+    test('constInstance should throw UnsupportedError', () {
+      final funcType = FunctionType();
+      expect(() => funcType.constInstance([]), throwsUnsupportedError);
+    });
+
+    test('constInstanceNamed should throw UnsupportedError', () {
+      final funcType = FunctionType();
+      expect(
+        () => funcType.constInstanceNamed('name', []),
+        throwsUnsupportedError,
+      );
+    });
+
+    test('should support toTypeDef', () {
+      final funcType = FunctionType(
+        (b) =>
+            b
+              ..returnType = refer('String')
+              ..requiredParameters.add(refer('int')),
+      );
+      expect(
+        funcType.toTypeDef('MyFunc'),
+        equalsDart('typedef MyFunc = String Function(int);', emitter),
+      );
+    });
+  });
+}

pkgs/code_builder/test/specs/record_type_test.dart

diff --git a/pkgs/code_builder/test/specs/record_type_test.dart b/pkgs/code_builder/test/specs/record_type_test.dart
index 55f5318..f840fe3 100644
--- a/pkgs/code_builder/test/specs/record_type_test.dart
+++ b/pkgs/code_builder/test/specs/record_type_test.dart
@@ -95,4 +95,39 @@
       equalsDart('(({int named, int other})?,)', emitter),
     );
   });
+
+  group('RecordType API contracts', () {
+    test('properties should be correct', () {
+      final recordType = RecordType();
+      expect(recordType.url, isNull);
+      expect(recordType.symbol, isNull);
+      expect(recordType.type, same(recordType));
+    });
+
+    test('newInstance should throw UnsupportedError', () {
+      final recordType = RecordType();
+      expect(() => recordType.newInstance([]), throwsUnsupportedError);
+    });
+
+    test('newInstanceNamed should throw UnsupportedError', () {
+      final recordType = RecordType();
+      expect(
+        () => recordType.newInstanceNamed('name', []),
+        throwsUnsupportedError,
+      );
+    });
+
+    test('constInstance should throw UnsupportedError', () {
+      final recordType = RecordType();
+      expect(() => recordType.constInstance([]), throwsUnsupportedError);
+    });
+
+    test('constInstanceNamed should throw UnsupportedError', () {
+      final recordType = RecordType();
+      expect(
+        () => recordType.constInstanceNamed('name', []),
+        throwsUnsupportedError,
+      );
+    });
+  });
 }

pkgs/code_builder/test/specs/type_reference_test.dart

diff --git a/pkgs/code_builder/test/specs/type_reference_test.dart b/pkgs/code_builder/test/specs/type_reference_test.dart
index 9291cad..5b2aa01 100644
--- a/pkgs/code_builder/test/specs/type_reference_test.dart
+++ b/pkgs/code_builder/test/specs/type_reference_test.dart
@@ -66,5 +66,75 @@
         equalsDart(r'List<int?>', emitter),
       );
     });
+
+    test('should support generic bound', () {
+      expect(
+        TypeReference(
+          (b) =>
+              b
+                ..symbol = 'T'
+                ..bound = refer('num'),
+        ),
+        equalsDart(r'T extends num', emitter),
+      );
+    });
+  });
+
+  group('TypeReference API', () {
+    final typeRef = TypeReference((b) => b..symbol = 'Foo');
+
+    test('properties should be exposed', () {
+      final localTypeRef = TypeReference(
+        (b) =>
+            b
+              ..symbol = 'Foo'
+              ..url = 'package:foo/foo.dart',
+      );
+      expect(localTypeRef.symbol, 'Foo');
+      expect(localTypeRef.url, 'package:foo/foo.dart');
+      expect(localTypeRef.type, same(localTypeRef));
+    });
+
+    test('should support newInstance', () {
+      expect(
+        typeRef.newInstance([literal(42)], {'bar': literal('baz')}, [
+          refer('int'),
+        ]),
+        equalsDart(r"Foo<int>(42, bar: 'baz', )"),
+      );
+    });
+
+    test('should support newInstanceNamed', () {
+      expect(
+        typeRef.newInstanceNamed(
+          'fromMap',
+          [literal(42)],
+          {'bar': literal('baz')},
+          [refer('int')],
+        ),
+        equalsDart(r"Foo.fromMap<int>(42, bar: 'baz', )"),
+      );
+    });
+
+    test('should support constInstance', () {
+      expect(
+        typeRef.constInstance([literal(42)], {'bar': literal('baz')}, [
+          refer('int'),
+        ]),
+        equalsDart(r"const Foo<int>(42, bar: 'baz', )"),
+      );
+    });
+
+    test('should support constInstanceNamed', () {
+      expect(
+        typeRef.constInstanceNamed(
+          'fromMap',
+          [literal(42)],
+          {'bar': literal('baz')},
+          [refer('int')],
+        ),
+        equalsDart(r"const Foo.fromMap<int>(42, bar: 'baz', )"),
+      );
+    });
   });
 }