F.I.R.S.T.

fast: tests should be fast
independent: tests should not depenend on each other
- one test should not set up the conditions for the next test
- test should be run independently and in any order you like
repeatable: tests should be runnable in any environment
- if your tests aren’t repeatable in any environment they you always have an excuse why the fail
self-validating: the tests should have a boolean output
- test either pass or fail
timely: test need to be written in a timely fashion
- unit tests should be written just before the production code that makes them pass
- if you write tests after production, then you may find the production code to be hard to test
- you may even decide that production code is not testable