Testing use of NSURLConnection with HTTP response error statuses

Question

I'm writing an iPhone application that needs to get some data from a web server. I'm using NSURLConnection to do the HTTP request, which works well, but I'm having trouble unit testing my code in the case where the response has an HTTP error code (like 404 or 500).

I'm using GTM for unit testing and OCMock for mocking.

When the server returns an error, the connection does not call connection:didFailWithError: on the delegate, but calls connection:didReceiveResponse:, connection:didReceiveData:, and connectionDidFinishLoading: instead. I'm currently checking the status code on the response in connection:didReceiveResponse: and calling cancel on the connection when the status code looks like an error to prevent connectionDidFinishLoading: from being called, where a successful response would be reported.

Providing a static stubbed NSURLConnection is simple, but I want my test to change it's behaviour when one of the mock connection's methods is called. Specifically, I want the test to be able to tell when the code has called cancel on the mock connection, so the test can stop calling connection:didReceiveData: and connectionDidFinishLoading: on the delegate.

Is there a way for tests to tell if cancel has been called on the mock object? Is there a better way to test code that uses NSURLConnection? Is there a better way to handle HTTP error statuses?

Answer 1

Is there a better way to handle HTTP error statuses?

I think you are on the right track. I use something similar to the following code, which I found here:

if ([response respondsToSelector:@selector(statusCode)])
{
    int statusCode = [((NSHTTPURLResponse *)response) statusCode];
    if (statusCode >= 400)
    {
        [connection cancel];  // stop connecting; no more delegate messages
        NSDictionary *errorInfo
          = [NSDictionary dictionaryWithObject:[NSString stringWithFormat:
            NSLocalizedString(@"Server returned status code %d",@""),
            statusCode]
                                        forKey:NSLocalizedDescriptionKey];
        NSError *statusError
          = [NSError errorWithDomain:NSHTTPPropertyStatusCodeKey
                                code:statusCode
                            userInfo:errorInfo];
        [self connection:connection didFailWithError:statusError];
    }
}

This cancels the connection, and calls connection:didFailWithError: in order to make http error codes behave exactly the same as any other connection error.