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

pkg/unittest/lib/src/test_environment.dart

Index: pkg/unittest/lib/src/test_environment.dart
diff --git a/pkg/unittest/lib/src/test_environment.dart b/pkg/unittest/lib/src/test_environment.dart
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+++ b/pkg/unittest/lib/src/test_environment.dart
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+// 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.
+
+part of unittest;
+
+/// Class for encapsulating test environment state.
+/// This is used by the withTestEnvironment method to support multiple
+/// invocations of the unittest library with the same application
+/// instance.
+class TestEnvironment {
+  Configuration config = null;
+
+  // We use a 'dummy' context for the top level to eliminate null
+  // checks when querying the context. This allows us to easily
+  //  support top-level setUp/tearDown functions as well.
+  final rootContext = new _GroupContext();
+  _GroupContext currentContext;
+
+  /// Represents the index of the currently running test case
+  /// == -1 implies the test system is not running
+  /// == [number of test cases] is a short-lived state flagging that the last
+  ///    test has completed
+  int currentTestCaseIndex = -1;
+
+  /// Whether the framework is in an initialized state.
+  bool initialized = false;
+
+  /// Time since we last gave non-sync code a chance to be scheduled.
+  int lastBreath = new DateTime.now().millisecondsSinceEpoch;
+
+  /// The set of tests to run can be restricted by using [solo_test] and
+  /// [solo_group].
+  /// As groups can be nested we use a counter to keep track of the nest level
+  /// of soloing, and a flag to tell if we have seen any solo tests.
+  int soloNestingLevel = 0;
+  bool soloTestSeen = false;
+
+  final List<TestCase> testCases = new List<TestCase>();
+
+  String uncaughtErrorMessage = null;
+
+  TestEnvironment() {
+    currentContext = rootContext;
+  }
+}