Changes

Third-party packages -- those not in python's stdlib -- should be introduced only if they provide considerable value to testing (e.g. ability to test what is otherwise not possible, considerable savings in code complexity/manhours, etc.). In general, adding a test-only dependency should be taken (nearly) as seriously as adding a mozbase package dependency via ''install_requires''. Required packages should, if at all possible, be pure python and of high quality. Preferably, test-required packages should be ad hoc standards if possible; for instance, if the package is slated to be included in the stdlib or is in a future python version, it is a good candidate.