如何测试异步方法？

Question

我有一个通过网络获取XML或JSON的对象。一旦获取完成，它就会调用选择器，传入返回的数据。所以，举个例子，我的代码是这样的：

-(void)testResponseWas200
{
    [MyObject get:@"foo.xml" withTarget:self selector:@selector(dataFinishedLoading:)];  
}

我尝试了在测试类中实现dataFinishedLoading的路线，并尝试在该方法中进行测试，但测试套件就是锁定了。这看起来像是一个嘲笑的案例，但我想知道其他人是否遇到过这种情况，以及他们是如何处理的。

仅供参考:我使用gh-unit进行测试，任何以test*为前缀的方法都会自动执行。

Answer 1

出现在脑海中的三种方式是: NSRunLoop、信号量和组。

NSRunLoop

__block bool finished = false;

// For testing purposes we create this asynchronous task 
// that starts after 3 seconds and takes 1 second to execute.
dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_LOW, 0UL);
dispatch_time_t threeSeconds = dispatch_time(DISPATCH_TIME_NOW, 3LL * NSEC_PER_SEC);
dispatch_after(threeSeconds, queue, ^{ 
    sleep(1); // replace this with your task
    finished = true; 
});

// loop until the flag is set from inside the task
while (!finished) {
    // spend 1 second processing events on each loop
    NSDate *oneSecond = [NSDate dateWithTimeIntervalSinceNow:1];
    [[NSRunLoop currentRunLoop] runMode:NSDefaultRunLoopMode beforeDate:oneSecond];
}

NSRunLoop是一个循环，它处理网络端口、键盘或您插入的任何其他输入源等事件，并在处理这些事件后或在一段时间限制后返回。当没有要处理的事件时，run循环使线程进入休眠状态。所有Cocoa和Core Foundation应用程序都有一个运行循环。你可以在苹果的线程编程指南：或Mike Ash 中阅读更多关于run循环的内容。

在这个测试中，我只是使用NSRunLoop让线程休眠一秒钟。如果没有它，while中的常量循环将消耗100%的CPU核心。

如果块和布尔标志是在相同的词法作用域中创建的(例如:都在一个方法中)，那么该标志需要__block storage qualifier是可变的。如果标志是一个全局变量，它就不需要它了。

如果在设置标志之前测试崩溃，线程将永远等待。添加一个时间限制来避免这种情况：

NSDate *timeout = [NSDate dateWithTimeIntervalSinceNow:2];
while (!finished && [timeout timeIntervalSinceNow]>0) {
    [[NSRunLoop currentRunLoop] runMode:NSDefaultRunLoopMode 
                             beforeDate:[NSDate dateWithTimeIntervalSinceNow:1]];
}
if (!finished) NSLog(@"test failed with timeout");

如果您正在使用此代码进行单元测试，则插入超时的另一种方法是使用断言分派一个块：

// taken from https://github.com/JaviSoto/JSBarrierOperationQueue/blob/master/JSBarrierOperationQueueTests/JSBarrierOperationQueueTests.m#L118
dispatch_time_t timeout = dispatch_time(DISPATCH_TIME_NOW, 2LL * NSEC_PER_SEC);
dispatch_after(timeout, dispatch_get_main_queue(), ^(void){
    STAssertTrue(done, @"Should have finished by now");
});

信号量

类似的想法，但休眠直到信号量改变，或直到时间限制：

dispatch_semaphore_t semaphore = dispatch_semaphore_create(0);

// signal the semaphore after 3 seconds using a global queue
dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_LOW, 0UL);
dispatch_after(dispatch_time(DISPATCH_TIME_NOW, 3LL*NSEC_PER_SEC), queue, ^{ 
    sleep(1);
    dispatch_semaphore_signal(semaphore);
});

// wait with a time limit of 5 seconds
dispatch_time_t timeout = dispatch_time(DISPATCH_TIME_NOW, 5LL*NSEC_PER_SEC);
if (dispatch_semaphore_wait(semaphore, timeout)==0) {
    NSLog(@"success, semaphore signaled in time");
} else {
    NSLog(@"failure, semaphore didn't signal in time");
}

dispatch_release(semaphore);

相反，如果我们一直在等待dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER);，我们就会被卡住，直到任务发出信号，它会一直在后台队列中运行。

组

现在想象一下，你必须等待几个街区。您可以使用int作为标志，或者创建一个以更高数字开头的信号量，或者您可以对块进行分组，并等待分组完成。在这个例子中，我只用了一个块就完成了后面的操作：

dispatch_group_t group = dispatch_group_create();
dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_LOW, 0UL);

// dispatch work to the given group and queue
dispatch_group_async(group,queue,^{
    sleep(1); // replace this with your task
});

// wait two seconds for the group to finish
dispatch_time_t timeout = dispatch_time(DISPATCH_TIME_NOW, 2LL*NSEC_PER_SEC);
if (dispatch_group_wait(group, timeout)==0) {
    NSLog(@"success, dispatch group completed in time");
} else {
    NSLog(@"failure, dispatch group did not complete in time");
}

dispatch_release(group);

如果出于某种原因(为了清理资源？)要在组完成后运行一个块，请使用dispatch_group_notify(group,queue, ^{/*...*/});

Answer 2

Answer 3

@jano谢谢你我从你的帖子里做了这个小工具

在PYTestsUtils.m中

+ (void)waitForBOOL:(BOOL*)finished forSeconds:(int)seconds {
    NSDate *timeout = [NSDate dateWithTimeIntervalSinceNow:seconds];
    while (!*finished && [timeout timeIntervalSinceNow]>0) {
        [[NSRunLoop currentRunLoop] runMode:NSDefaultRunLoopMode
                                 beforeDate:[NSDate dateWithTimeIntervalSinceNow:1]];
    }
}

在我的测试文件

- (void)testSynchronizeTime
{
    __block BOOL finished = NO;
    [self.connection synchronizeTimeWithSuccessHandler:^(NSTimeInterval serverTime) {
        NSLog(@"ServerTime %f", serverTime);
        finished = YES;
    } errorHandler:^(NSError *error) {
        STFail(@"Cannot get ServerTime %@", error);
        finished = YES;
    }];

    [PYTestsUtils waitForBOOL:&finished forSeconds:10];
    if (! finished)
        STFail(@"Cannot get ServerTime within 10 seconds");

}

变化

添加PYTestsUtils.m

+ (void)execute:(PYTestExecutionBlock)block ifNotTrue:(BOOL*)finished afterSeconds:(int)seconds {
    [self waitForBOOL:finished forSeconds:seconds];
    if (! *finished) block();
}

用法：

- (void)testSynchronizeTime
{
    __block BOOL finished = NO;
    [self.connection synchronizeTimeWithSuccessHandler:^(NSTimeInterval serverTime) {
        NSLog(@"ServerTime %f", serverTime);
        finished = YES;
    } errorHandler:^(NSError *error) {
        STFail(@"Cannot get ServerTime %@", error);
        finished = YES;
    }];

    [PYTestsUtils execute:^{
        STFail(@"Cannot get ServerTime within 10 seconds");
    } ifNotTrue:&finished afterSeconds:10];

}