If you're looking for a full-featured IDE, I don't think you need to look any further than PyCharm, however, Sublime with it's PEP 8 Linter, and CodeIntel plugins will give you a lighter-weight yet effective solution.
You can even run your tests in Sublime's console if that's something you'd want to do, or use the terminal (as I ended up doing).
Similarly, for vim as people have pointed out, if that's something you're more comfortable with.
I've tried pretty much everything, and PyCharm has been the nicest, most productive set-up for me. It features a really nice integrated debugger, a test runner, dependency checking/management and really good code analysis/autocomplete/refactoring.
And the reverse for me, its just the classic CLI vs GUI personal preference. Every time I touch the mouse in PyCharm, I cringe with the feeling of delay. Python since 2001 here, so there wasn't much GUI python until recently, perhaps I've fallen into a trap :)
Here is some video of myself programming some very boring stuff in python/vim, https://www.livecoding.tv/jquast/ which unfortunately looks like it requires anybody to login/signup to watch, probably won't be using this service again.
You can even run your tests in Sublime's console if that's something you'd want to do, or use the terminal (as I ended up doing).
Similarly, for vim as people have pointed out, if that's something you're more comfortable with.