I recently started developing for Google App Engine after several years working with Rails, and my sense is that Python testing (at least on App Engine) is seriously behind the Ruby/Rails world.

GAE is especially hard to test because you essentially run it in an emulator locally. It's also pretty bare-bones, so you don't get the free testing tools you get with Rails, like fixtures (love 'em or hate 'em, at least they can get you started) and a test runner.

Sure, you can set all that stuff up (and I do) but it sucks having to do a bunch of grunt work that's done for you in Rails.

FWIW, my preferred testing setup in Rails is Shoulda with Mocha for mocking and my own fixie library for pre-populating test data (it's faster than factory_girl) and factory_girl if I find I need it. I think acceptance testing with Cucumber is over rated and I'll be damned if I'm going to program in English, so I do not bother.

For GAE, I'm using gaetestbed and writing a lot of helper functions.