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

pkg/matcher/lib/src/future_matchers.dart

-// Copyright (c) 2012, 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 matcher.future_matchers;
-
-import 'dart:async';
-
-import 'expect.dart';
-import 'interfaces.dart';
-import 'util.dart';
-
-/// Matches a [Future] that completes successfully with a value.
-///
-/// Note that this creates an asynchronous expectation. The call to `expect()`
-/// that includes this will return immediately and execution will continue.
-/// Later, when the future completes, the actual expectation will run.
-///
-/// To test that a Future completes with an exception, you can use [throws] and
-/// [throwsA].
-final Matcher completes = const _Completes(null, '');
-
-/// Matches a [Future] that completes succesfully with a value that matches
-/// [matcher].
-///
-/// Note that this creates an asynchronous expectation. The call to
-/// `expect()` that includes this will return immediately and execution will
-/// continue. Later, when the future completes, the actual expectation will run.
-///
-/// To test that a Future completes with an exception, you can use [throws] and
-/// [throwsA].
-///
-/// [id] is an optional tag that can be used to identify the completion matcher
-/// in error messages.
-Matcher completion(matcher, [String id = '']) =>
-    new _Completes(wrapMatcher(matcher), id);
-
-class _Completes extends Matcher {
-  final Matcher _matcher;
-  final String _id;
-
-  const _Completes(this._matcher, this._id);
-
-  bool matches(item, Map matchState) {
-    if (item is! Future) return false;
-    var done = wrapAsync((fn) => fn(), _id);
-
-    item.then((value) {
-      done(() { if (_matcher != null) expect(value, _matcher); });
-    }, onError: (error, trace) {
-      var id = _id == '' ? '' : '${_id} ';
-      var reason = 'Expected future ${id}to complete successfully, '
-                   'but it failed with ${error}';
-      if (trace != null) {
-        var stackTrace = trace.toString();
-        stackTrace = '  ${stackTrace.replaceAll('\n', '\n  ')}';
-        reason = '$reason\nStack trace:\n$stackTrace';
-      }
-      done(() => fail(reason));
-    });
-
-    return true;
-  }
-
-  Description describe(Description description) {
-    if (_matcher == null) {
-      description.add('completes successfully');
-    } else {
-      description.add('completes to a value that ').addDescriptionOf(_matcher);
-    }
-    return description;
-  }
-}