In unit test, execute the block passed in queue with dispatch_asyc

问题

If I dispatch_async a block on main queue like this:

-(void) myTask {
  dispatch_async(dispatch_get_main_queue(), ^{
      [self.service fetchData];
   });
}

In unit test, I can execute the block passed in main queue by manually run the main loop like this:

-(void)testMyTask{
  // call function under test
  [myObj myTask];
  // run the main loop manually!
  [[NSRunLoop mainRunLoop] runUntilDate:[NSDate dateWithTimeIntervalSinceNow:0.01]];
  // now I can verify the function 'fetchData' in block is called
  ...
}

Now, I have another similar function which dispatch block to an sequential queue other than main queue:

-(void) myTask2 {
  dispatch_async(dispatch_queue_create("my.sequential.queue", NULL), ^{
      [self.service fetchData];
   });
}

In unit test, how can I execute the block manually now?

-(void)testMyTask2{
  // call function under test
  [myObj myTask2];
  // How to manually execute the block now?
}

=== Clarify ===

The reason why I want to manually execute is because I don't like any Wait-For-Timeout way doing the test. Because waiting time is depending on CPU speed, on different machines could be different. I'd like to manually execute the block passed to queue (the same way as how I did for the main queue test case) and then verify the result.

回答1:

You could create the queue in your test function.

-(void) myTask2:(dispatch_queue_t*)queue {
    dispatch_async(*queue, ^{
        [self.service fetchData];
    });
}

-(void)testMyTask2{
    dispatch_queue_t queue = dispatch_queue_create("my.sequential.queue", NULL);
    [myObj myTask2:&queue];

    dispatch_sync(queue, ^{
    });
}

(Just realised currentRunLoop is not needed)

回答2:

For execute test in async block use XCTestExpectation class

-(void) myTask2 {
  XCTestExpectation *expectation = [self expectationWithDescription:@"catch is called"];
  dispatch_async(dispatch_queue_create("my.sequetial.queue", NULL), ^{
      [self.serviceClient fetchDataForUserId:self.userId];
      [expectation fulfill];
   });

   [self waitForExpectationsWithTimeout:Timeout handler:^(NSError *error) {
        //check that your NSError nil or not
    }];
}

Hope this help

来源：https://stackoverflow.com/questions/37992319/in-unit-test-execute-the-block-passed-in-queue-with-dispatch-asyc