Add a ScheduledProcess class to pkg/scheduled_test.

pkg/scheduled_test/lib/src/scheduled_future_matchers.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.
+
+library scheduled_future_matchers;
+
+import 'dart:async';
+
+import '../scheduled_test.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].
+///
+/// This differs from the `completes` matcher in `unittest` in that it pipes any
+/// errors in the Future to [currentSchedule], rather than reporting them in the
+/// [expect]'s error message.
+Matcher completes = const _ScheduledCompletes(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].
+///
+/// This differs from the `completion` matcher in `unittest` in that it pipes
+/// any errors in the Future to [currentSchedule], rather than reporting them in
+/// the [expect]'s error message.
+Matcher completion(matcher) => new _ScheduledCompletes(wrapMatcher(matcher));
+
+class _ScheduledCompletes extends BaseMatcher {
+  final Matcher _matcher;
+
+  const _ScheduledCompletes(this._matcher);
+
+  bool matches(item, MatchState matchState) {
+    if (item is! Future) return false;
+
+    wrapFuture(item.then((value) {
+      if (_matcher != null) expect(value, _matcher);
+    }));
+
+    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;
+  }
+}