Re-apply "Remove unittest and matcher from the repo."

pkg/unittest/lib/src/test_environment.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.
-
-part of unittest;
-
-/// Class for encapsulating test environment state.
-///
-/// This is used by the [withTestEnvironment] method to support multiple
-/// invocations of the unittest library within the same application
-/// instance.
-class _TestEnvironment {
-  Configuration config;
-
-  // 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;
-
-  /// The [currentTestCaseIndex] represents the index of the currently running
-  /// test case.
-  ///
-  /// If this is -1 it implies the test system is not running.
-  /// It will be set to [number of test cases] as a short-lived state flagging
-  /// that the last test has completed.
-  int currentTestCaseIndex = -1;
-
-  /// The [initialized] variable specifies whether the framework
-  /// has been initialized.
-  bool initialized = false;
-
-  /// The time since we last gave asynchronous 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 nesting
-  /// level of soloing, and a flag to tell if we have seen any solo tests.
-  int soloNestingLevel = 0;
-  bool soloTestSeen = false;
-
-  /// The list of test cases to run.
-  final List<TestCase> testCases = new List<TestCase>();
-
-  /// The [uncaughtErrorMessage] holds the error messages that are printed
-  /// in the test summary.
-  String uncaughtErrorMessage;
-
-  _TestEnvironment() {
-    currentContext = rootContext;
-  }
-}