How to write docstrings for tests

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A lot of projects I contribute to insist that tests have comments or docstrings in them. If ever you’re working on a project that has a similar requirement, and you’re struggling to write docstrings for your tests, here’s a handy five-step guide:

  1. Write the first docstring that comes to mind. It will almost certainly be:

    """Test that input is parsed correctly."""
  2. Get rid of “Test that” or “Check that”. We know it’s a test.

    """Input should be parsed correctly."""
  3. Seriously?! Why’d you have to go and add “should”? It’s a test, it’s all about “should”.

    """Input is parsed correctly."""
  4. Correctly”, “properly”, and “as we expect” are all redundant. Axe them too.

    """Input is parsed."""
  5. Look at what’s left. Is it saying anything at all? If so, great. If not, consider adding something specific about the test behaviour and perhaps even why it’s desirable behaviour to have.

    Input is parsed into an immutable dict according to the config
    schema, so we get config info without worrying about input
    validation all the time.

Happy hacking!

Originally published as a post on Google+.