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 'dart:async';
+import 'package:unittest/unittest.dart';
+
+Future runUnittests(Function callback) {
+  var config = new UnittestConfiguration();
+
+  unittestConfiguration = config;
+  callback();
+
+  return config.done;
+}
+
+class UnittestConfiguration extends SimpleConfiguration {
+  final Completer _completer = new Completer();
+
+  Future get done => _completer.future;
+
+  onDone(success) {
+    new Future.sync(() {
+      super.onDone(success);
+    }).then((_) => _completer.complete(_))
+    .catchError((error, stack) => _completer.completeError(error, stack));
+  }
+}
+
+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';
+  } catch(error) {
+    if (error is! StateError)
+      throw 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));
+}