Unit testing with NSURLConnection

Question

Hello!

I want to test a piece of code that uses network (the NSURLConnection class, to be specific). The code (let’s call it NetworkManager) looks a bit like this:

- (id) buildConnection
{
    // some more code and then:
    return [NSURLConnection …];
}

- (void) startNetworkSync
{
    id connection = [self buildConnection];
    //…
}

In the unit test I would like to get rid of the networking, ie. replace the NSURLConnection object by a mock. How do I do this?

I’ve tried creating a partial mock of the NetworkManager that would replace the buildConnection method by a stub. The problem is that partial mocks as done by OCMock only stub messages from the outside world – sending buildConnection from the startNetworkSync invokes the original method, not the stub.

I have also tried monkey-patching the NetworkManager class through a category. This works, I can easily override the buildConnection method by other code and replace the real NSURLConnection with a stub. The problem is that I found no simple way I could get the stubbed connection in the test – the connection is a private part of the NetworkManager.

Then I could subclass the NetworkManager, override the buildConnection method and add an instance variable plus an accessor for the created connection. This seems like a lot of code, though.

How would you solve this? I am looking for a solution that keeps the NetworkManager class design clean and does not require much magic nor much code in the test.

Answer 1

This is the kind of thing dependency injection is designed to solve; if you use startNetworkSyncWithConnection:(NSURLConnection*) instead you can easily test the method with a mock connection. If you don't want to change the API for your clients you could even keep startNetworkSync as a wrapper that does nothing but call that new method with [self buildConnection] as the argument.

Answer 2

I modified OCMock to support real partial mocks. You can find the code at http://github.com/mmangino/OCMock/tree/master

Mike