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

pkg/unittest/lib/src/test_case.dart

 // Copyright (c) 2013, 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.
 
 part of unittest;
 
 /// Represents the state for an individual unit test.
 ///
 /// Create by calling [test] or [solo_test].
 class TestCase {
@@ skipping 42 matching lines @@
 
   bool _enabled = true;
 
   bool get enabled => _enabled;
 
   bool _doneTeardown = false;
 
   Completer _testComplete;
 
   TestCase._internal(this.id, this.description, this._testFunction)
-      : currentGroup = _currentContext.fullName,
-        _setUp = _currentContext.testSetup,
-        _tearDown = _currentContext.testTeardown;
+      : currentGroup = _environment.currentContext.fullName,
+        _setUp = _environment.currentContext.testSetup,
+        _tearDown = _environment.currentContext.testTeardown;
 
   bool get isComplete => !enabled || result != null;
 
   Function _errorHandler(String stage) => (e, stack) {
     if (stack == null && e is Error) {
       stack = e.stackTrace;
     }
     if (result == null || result == PASS) {
       if (e is TestFailure) {
         _fail("$e", stack);
@@ skipping 106 matching lines @@
   }
 
   void _markCallbackComplete() {
     if (--_callbackFunctionsOutstanding == 0 && !isComplete) {
       _pass();
     }
   }
 
   String toString() => _result != null ? "$description: $result" : description;
 }