I am writing some QUnit tests for a JavaScript that makes AJAX calls.
For isolation I overwrite $.ajax to write the parameter array of an AJAX call to a
Look at the jQuery documentation: You'll see that the Ajax setup provides a number of other conditions that are tested for. If you make them all point to your fakeAjaxSuccess, you might achieve for your objective.
Alternatively, wrap your $.ajax call into its own function and have whatever calls it simply call your event handler with the fakeAjaxSuccess object.