Add regression test for relative imports in tests under lib

integration_tests/regression/dart_test.yaml

@@ -0,0 +1,13 @@
+paths:
+- lib/issue_2142/test.dart
+
+platforms:
+- chrome
+- vm
+
+compilers:
+- dart2js
+- dart2wasm
+- exe
+- kernel
+- source

integration_tests/regression/lib/issue_2142/import.dart

@@ -0,0 +1,8 @@
+// Copyright (c) 2023, 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: prefer_relative_imports
+import 'package:regression_tests/issue_2142/test.dart';
+
+Thing newThing() => Thing();

integration_tests/regression/lib/issue_2142/test.dart

@@ -0,0 +1,17 @@
+// Copyright (c) 2023, 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.
+
+@Skip('https://github.com/dart-lang/test/issues/2142')
+library;
+
+import 'package:test/test.dart';
+import 'import.dart';
+
+void main() {
+  test('aThing is a Thing', () {
+    expect(newThing(), isA<Thing>());
+  });
+}
+
+class Thing {}

integration_tests/regression/mono_pkg.yaml

@@ -0,0 +1,15 @@
+# See https://pub.dev/packages/mono_repo
+
+sdk:
+- dev
+
+os:
+- linux
+
+stages:
+- analyze_and_format:
+  - group:
+    - format
+    - analyze: --fatal-infos
+- unit_test:
+  - test

integration_tests/regression/pubspec.yaml

@@ -0,0 +1,15 @@
+name: regression_tests
+publish_to: none
+environment:
+  sdk: ^3.0.0
+dependencies:
+  test: any
+dev_dependencies:
+  dart_flutter_team_lints: ^2.1.1
+dependency_overrides:
+  test:
+    path: ../../pkgs/test
+  test_api:
+    path: ../../pkgs/test_api
+  test_core:
+    path: ../../pkgs/test_core

integration_tests/wasm/pubspec.yaml

@@ -3,6 +3,7 @@ publish_to: none
 environment:
   sdk: ^3.0.0
 dev_dependencies:
+  dart_flutter_team_lints: ^2.1.1
   test: any
 dependency_overrides:
   test:

integration_tests/wasm/test/hello_world_test.dart

@@ -6,6 +6,8 @@
 @TestOn('wasm')
 // This retry is a regression test for https://github.com/dart-lang/test/issues/2006
 @Retry(2)
+library;
+
 import 'package:test/test.dart';
 
 void main() {