Support future matchers and expectAsync in tearDowns.

lib/src/backend/outstanding_callback_counter.dart

+// Copyright (c) 2015, 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 test.backend.outstanding_callback_counter;
+
+import 'dart:async';
+
+/// A class that counts outstanding callbacks for a test and fires a future once
+/// they reach zero.
+///
+/// The outstanding callback count automatically starts at 1.
+class OutstandingCallbackCounter {
+  /// The number of outstanding callbacks.
+  var _count = 1;

[kevmoo, 2015/04/28 18:44:49]

int!

[nweiz, 2015/04/28 18:56:18]

It's private and its type is obvious from its initializer.

+
+  /// A future that fires when the oustanding callback count reaches 0.
+  Future get noOutstandingCallbacks => _completer.future;
+  final _completer = new Completer();
+
+  /// Adds an outstanding callback.
+  void addOutstandingCallback() {
+    _count++;
+  }
+
+  /// Removes an outstanding callback.
+  void removeOutstandingCallback() {
+    _count--;
+    if (_count != 0) return;
+    if (_completer.isCompleted) return;
+    _completer.complete();
+  }
+
+  /// Removes all outstanding callbacks, forcing [noOutstandingCallbacks] to
+  /// fire.
+  ///
+  /// Future calls to [addOutstandingCallback] and [removeOutstandingCallback]
+  /// will be ignored.
+  void removeAllOutstandingCallbacks() {
+    if (!_completer.isCompleted) _completer.complete();
+  }
+}