Testing your ExtJS 3.4 components with Jasmine

Developing your own ExtJS components for your application is more fun and results into more resilient code if you write them hand-in-hand with test code. A solid test basis can also facilitate the task of refactoring your software.

Although, test driven development is easy for javascript code, how can ExtJS 3.4 components be tested? Which parts of our components should be tested to accomplish a successful refactoring?