Enhance the Dart unittest library to support multiple invocations in the same application run.

pkg/unittest/test/with_test_environment_test.dart

+// Copyright (c) 2014, 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.
+
+library unittest.with_test_environment_test;
+
+import 'package:unittest/unittest.dart';
+
+void runUnittests(Function callback) {
+  unittestConfiguration = new SimpleConfiguration();
+  callback();
+}
+
+void runTests() {
+  test('test', () => expect(2 + 3, equals(5)));
+}
+
+void runTests1() {
+  test('test1', () => expect(4 + 3, equals(7)));
+}
+
+// Test that we can run two different sets of tests in the same run using the
+// withTestEnvironment method.
+void main() {
+  // First check that we cannot call runUnittests twice in a row without it
+  // throwing a StateError due to the unittestConfiguration being set globally
+  // in the first call.
+  try {
+    runUnittests(runTests);
+    runUnittests(runTests1);
+    throw 'Expected this to be unreachable since 2nd run above should throw';
+  } on StateError catch (error) {
+    // expected, silently ignore.
+  }
+
+  // Second test that we can run both when encapsulating in their own private
+  // test environment.
+  withTestEnvironment(() => runUnittests(runTests));
+  withTestEnvironment(() => runUnittests(runTests1));
+
+  // Third test that we can run with two nested test environments.
+  withTestEnvironment(() {
+    runUnittests(runTests);
+    withTestEnvironment(() {
+      runUnittests(runTests1);
+    });
+  });
+}