How to unit an objective C class with an async callback.

ExampleUnitTest.m

- (void)testAsyncExample
{
    dispatch_semaphore_t semaphore = dispatch_semaphore_create(0);
    __block BOOL hasRunBlock = NO;
    
    [MyClass asyncCallback:^{
        
        hasRunBlock = YES;
        dispatch_semaphore_signal(semaphore);
    }];
    
    double timeoutDelayInSeconds = 1.0;
    dispatch_time_t timeout = dispatch_time(DISPATCH_TIME_NOW,
                                            (int64_t)(timeoutDelayInSeconds * NSEC_PER_SEC));
    long result = dispatch_semaphore_wait(semaphore, timeout);
    XCTAssertTrue(result == 0, @"Timed out waiting for semaphore");
    
    XCTAssertTrue(hasRunBlock, @"");
}