Piotr:
You might be interested in the work I've done with Mimic, a network stubbing tool written in Ruby which lets you stub requests at a high-level and can be used from your Objective-C using the supplied wrapper.
With regards to asynchronous testing, please take a look at a little utility I wrote called AssertEventually.
This example shows both Mimic and assertEventually in action.
In addition, you might want to look at Kiwi - it's a great little Objective-C testing framework that is built on top of OCUnit. I recently contributed a patch to port my AssertEventually behaviour over to Kiwi which lets you write things like:
id someObject = nil;
[do SomethingThatFetchesSomeObjectAsynchronously];
[[theObject(&someObject) shouldEventually] equal:@"some result"];
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