blob: 961d1d61c725bcc1ab97adbe15092750359f1e08 [file] [log] [blame]
// 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.
/// This library is used for testing asynchronous tests.
/// If a test is asynchronous, it needs to notify the testing driver
/// about this (otherwise tests may get reported as passing [after main()
/// finished] even if the asynchronous operations fail).
/// Tests which can't use the unittest framework should use the helper functions
/// in this library.
/// This library provides four methods
/// - asyncStart(): Needs to be called before an asynchronous operation is
/// scheduled.
/// - asyncEnd(): Needs to be called as soon as the asynchronous operation
/// ended.
/// - asyncSuccess(_): Variant of asyncEnd useful together with Future.then.
/// - asyncTest(f()): Helper method that wraps a computation that returns a
/// Future with matching calls to asyncStart() and
/// asyncSuccess(_).
/// After the last asyncStart() called was matched with a corresponding
/// asyncEnd() or asyncSuccess(_) call, the testing driver will be notified that
/// the tests is done.
library async_helper;
import 'dart:async';
bool _initialized = false;
int _asyncLevel = 0;
Exception _buildException(String msg) {
return new Exception('Fatal: $msg. This is most likely a bug in your test.');
/// Call this method before an asynchronous test is created.
/// If [count] is provided, expect [count] [asyncEnd] calls instead of just one.
void asyncStart([int count = 1]) {
if (count <= 0) return;
if (_initialized && _asyncLevel == 0) {
throw _buildException('asyncStart() was called even though we are done '
'with testing.');
if (!_initialized) {
_initialized = true;
_asyncLevel += count;
/// Call this after an asynchronous test has ended successfully.
void asyncEnd() {
if (_asyncLevel <= 0) {
if (!_initialized) {
throw _buildException('asyncEnd() was called before asyncStart().');
} else {
throw _buildException('asyncEnd() was called more often than '
if (_asyncLevel == 0) {
* Call this after an asynchronous test has ended successfully. This is a helper
* for calling [asyncEnd].
* This method intentionally has a signature that matches [:Future.then:] as a
* convenience for calling [asyncEnd] when a [:Future:] completes without error,
* like this:
* asyncStart();
* Future result = test();
* result.then(asyncSuccess);
void asyncSuccess(_) => asyncEnd();
* Helper method for performing asynchronous tests involving [:Future:].
* [f] must return a [:Future:] for the test computation.
Future<void> asyncTest(f()) {
return f().then(asyncSuccess);