Xcode testing AFNetwork Operation callback blocks

Just recently, I was writing some tests in Xcode for some HTTP requests using the AFNetwork library. Previously I’ve used the ASIHTTPRequest library, but in this particular project, I’ve chosen to use AFNetworking for its JSON support.

Since the requests run asynchronously we need a way to wait for the operation to complete. This is easy:

- (void)testRequest
{
    MyHTTPClient* api = [MyHTTPClient sharedInstance]; // subclass of AFHTTPClient
    NSDictionary* parameters = [NSDictionary dictionary]; // add query parameters to this dict.
    __block int status = 0;
    AFJSONRequestOperation* request = [api getPath:@"path/to/test"
                                        parameters:parameters
                                           success:^(AFHTTPRequestOperation *operation, id responseObject) {
                                               // success code
                                               status = 1;
                                               NSLog(@"succeeded");
                                           } failure:^(AFHTTPRequestOperation *operation, NSError *error) {
                                               // failure
                                               status = 2;
                                               NSLog(@"failed");
                                           }];
    [api enqueueHTTPRequestOperation:request];
    [api.operationQueue waitUntilAllOperationsAreFinished];

    STAssertTrue([request isFinished], @"request finished");
    STAssertEquals(request.response.statusCode, 200, @"request returned 200 OK");
    STAssertEquals(status, 1, @"success block was executed");
}

This is great for testing that the request completes, and verifying its status. But if we need to test anything in the success or failure callbacks, the last test will fail with `status == 0`.

This is because AFNetwork processes its response in a background thread, and the final success or failure block callback is dispatched asynchronously from there to a specific queue, which unless provided is the main queue. This means that the block won’t get called until *AFTER* the test code has completed.

Putting in some kind of a lock causes a deadlock, since the test is running on the main thread, and the block callback never gets an opportunity to run. The solution is to manually run the main threads runloop until the callbacks have been processed.

Here’s my solution:

- (void)testRequest
{
    MyHTTPClient* api = [MyHTTPClient sharedInstance]; // subclass of AFHTTPClient
    NSDictionary* parameters = [NSDictionary dictionary]; // add query parameters to this dict.
    __block int status = 0;
    AFJSONRequestOperation* request = [api getPath:@"path/to/test"
                                        parameters:parameters
                                           success:^(AFHTTPRequestOperation *operation, id responseObject) {
                                               // success code
                                               status = 1;
                                               NSLog(@"succeeded");
                                           } failure:^(AFHTTPRequestOperation *operation, NSError *error) {
                                               // failure
                                               status = 2;
                                               NSLog(@"failed");
                                           }];
    [api enqueueHTTPRequestOperation:request];
    [api.operationQueue waitUntilAllOperationsAreFinished];

    while (status == 0)
    {
        // run runloop so that async dispatch can be handled on main thread AFTER the operation has 
        // been marked as finished (even though the call backs haven't finished yet).
        [[NSRunLoop currentRunLoop] runMode:NSDefaultRunLoopMode
                                 beforeDate:[NSDate date]];
    }

    STAssertTrue([request isFinished], @"request finished");
    STAssertEquals(request.response.statusCode, 200, @"request returned 200 OK");
    STAssertEquals(status, 1, @"success block was executed");
}

This addition will continually pump that run loop which allows AFNetwork’s async dispatch of the block to the main queue to execute, and hey presto! We now have a test that can also verify code in the success (or failure) completion blocks of an AFNetwork request operation.