My current thinking is that if you are writing larger JS components, it makes sense to pull out a set of interrelated behaviors both into a jQuery plugin and a set of tests for it.
But from the examples you mentioned, it sounds like you’re really looking for a level of protection within your integrated website. A tool like Selenium will probably be more powerful and appropriate for you. In particular, it
- can be automated
- can run against multiple browsers, including IE
- runs within the context of your web app and pages, so drag-n-drop can be tested where it really happens instead of in some test environment.
- AJAX can be tested