如何测试异步方法？ [英] How do you test an asynchronous method?
问题描述
我有一个对象通过网络获取XML或JSON。一旦这个抓取完成，它调用一个选择器，传入返回的数据。所以，例如我会有像：
- （void）testResponseWas200
{
[ MyObject get：@foo.xmlwithTarget：self selector：@selector（dataFinishedLoading :)];
}
我尝试在Test类中实现dataFinishedLoading的路由，那个方法，但是测试套件只是锁定。这似乎是一个嘲笑的情况，但我想知道，如果其他人遇到这个和如何处理它。
FYI：我使用gh单位
想到的三种方法是：NSRunLoop，semaphores和
NSRunLoop
__ block bool finished = false;
//为了测试的目的，我们创建这个异步任务
//在3秒后开始，需要1秒执行。
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）; //将此替换为你的任务
finished = true;
}）;
//循环，直到从任务内部设置标志
while（！finished）{
//每个循环上花费1秒处理事件
NSDate * oneSecond = [NSDate dateWithTimeIntervalSinceNow：1];
[[NSRunLoop currentRunLoop] runMode：NSDefaultRunLoopMode beforeDate：oneSecond];
}
NSRunLoop是一个循环，处理网络端口，键盘或任何您插入的其他输入源，并在处理这些事件后或在时间限制后返回。当没有要处理的事件时，运行循环使线程进入睡眠状态。所有Cocoa和Core Foundation应用程序都有一个运行循环。您可以在Apple的线程编程指南中了解有关运行循环的更多信息：运行循环 或在Mike Ash Friday Q& A 2010-01-01：NSRunLoop Internals 。
在这个测试中，我只是使用NSRunLoop来休眠线程一秒钟。没有它， while 中的常量循环将占用CPU内核的100％。
布尔标志在同一个词法范围内创建（例如：在方法内部），那么该标志需要 __ block 存储限定符。如果标志是一个全局变量，它不会需要它。
如果测试在设置标志前崩溃，线程将永远等待。添加时间限制以避免：
NSDate * timeout = [NSDate dateWithTimeIntervalSinceNow：2]
while（！complete&& [timeout timeIntervalSinceNow]> 0）{
[[NSRunLoop currentRunLoop] runMode：NSDefaultRunLoopMode
beforeDate：[NSDate dateWithTimeIntervalSinceNow：1]
}
if（！finished）NSLog（@test failed with timeout）;
如果您使用此代码进行单元测试，则插入超时的另一种方法是调度用assert阻止：
//取自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）;
}）;
Semaphore
改变或者直到时间限制：
dispatch_semaphore_t semaphore = dispatch_semaphore_create（0）;
//使用全局队列在3秒后通知信号量
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）;
}
//等待时间限制为5秒
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 did not signal in time）;
}
dispatch_release（semaphore）;如果相反，我们用 dispatch_semaphore_wait（semaphore，DISPATCH_TIME_FOREVER）永久等待;
组
b $ b 现在想象你必须等待几个街区。您可以使用int作为标志，也可以创建以更高的数字开头的信号量，或者可以分组块，然后等待组完成。在这个例子中，我只做一个块：
dispatch_group_t group = dispatch_group_create
dispatch_queue_t queue = dispatch_get_global_queue（DISPATCH_QUEUE_PRIORITY_LOW，0UL）;
//将工作分派到给定的组和队列
dispatch_group_async（group，queue，^ {
sleep（1）; //将此替换为任务
}）;
//等待两秒完成组
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（@失败，调度组没有及时完成）;
}
dispatch_release（group）;
如果由于某种原因（清理资源？），完成后，使用 dispatch_group_notify（group，queue，^ {/*...*/}）;
I have an object that fetches XML or JSON over a network. Once this fetching is complete it calls a selector, passing in the returned data. So, for example I'd have something like:
-(void)testResponseWas200
{
[MyObject get:@"foo.xml" withTarget:self selector:@selector(dataFinishedLoading:)];
}
I tried the route of implementing dataFinishedLoading in the Test class and attempting to test inside that method, but the test suite is just locking up. This seems like it's a case for mocking, but I'm wondering if others have encountered this and how they handled it.
FYI: I'm using gh-unit for testing and any method prefixed with test* is executed automatically.
解决方案 Three ways that come to mind are: NSRunLoop, semaphores, and groups.
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];
}
A NSRunLoop is a loop that processes events like network ports, keyboard, or any other input source you plug in, and returns after processing those events, or after a time limit. When there are no events to process, the run loop puts the thread to sleep. All Cocoa and Core Foundation applications have a run loop underneath. You can read more about run loops in Apple's Threading Programming Guide: Run Loops, or in Mike Ash Friday Q&A 2010-01-01: NSRunLoop Internals.
In this test, I'm just using the NSRunLoop to sleep the thread for a second. Without it, the constant looping in the while would consume 100% of a CPU core.
If the block and the boolean flag are created in the same lexical scope (eg: both inside a method), then the flag needs the __block storage qualifier to be mutable. Had the flag been a global variable, it wouldn't need it.
If the test crashes before setting the flag, the thread is stuck waiting forever. Add a time limit to avoid that:
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");
If you are using this code for unit testing, an alternative way to insert a timeout is to dispatch a block with an assert:
// 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");
});
Semaphore
Similar idea but sleeping until a semaphore changes, or until a time limit:
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);
If instead we waited forever with dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER); we would be stuck until getting a signal from the task, which keeps running on the background queue.
Group
Now imagine you have to wait for several blocks. You can use an int as flag, or create a semaphore that starts with a higher number, or you can group the blocks and wait until the group is finished. In this example I do the later with just one block:
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);
If for some reason (to clean up resources?) you want to run a block after the group is finished, use dispatch_group_notify(group,queue, ^{/*...*/});
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