Speed up tests

[bcomnes]

These tests take way to long to run. Some ideas for speeding up testing:

• Switch to tap. This is probably not going to help with speed, other than writing and maintaining tests.
• Remove sync calls wherever possible.
• Run tests in temp dirs where they won't overlap, so we can run them in parallel.
• Take the opportunity to improve assertion output.

Those are the main ideas I have for now.