@kenspirit does a nice job in this series (part 1 and part 2) of blog posts talking about some of the pain points (Stores, Ajax handling) of unit testing ExtJS applications. While @kenspirit provides a nice adaptation of jasmine-ajax for ExtJs (as jasmine-ajax only supports JQuery and Prototype currently), that adaptation does not work with ExtJS4. The following updated version should work - at least for basic Ajax mocking. Let me know if you have issues and I can (futher) update and improve upon this latest adaptation.