Software is kind of cool in that you can write programs that verify that your other programs work correctly. These testing "meta programs" tend to get short-shrift though, because it's not like the code is actually part of the shipping product. So who cares about cleanliness or good style or all that stuff?

I'd propose that a good rule (or at least guideline) for test code is:

Treat it like production code.

That means things like:

• Keep methods short
• Name things appropriately
• Avoid duplication (like copying and pasting big chunks of code)
• Add comments if the code isn't self-explanatory for some reason
• Readability counts
• etc.

The main justification is that the tests need to be correct and maintainable too, and all the things we've learned about good code contribute to those objectives. A large body of unmaintainable tests starts to become a liability rather than an asset. The one concession I'd make is that tests pretty much never require their own tests, because then you have a problem of infinite recursion.