Skip to main content

PyCon: Testing Tools in Python

I went to a two hour tutorial on testing. It was everything I hoped for. It was given by Grig Gheorghiu and Dr. C. Titus Brown. Here's an outline:
  • Unit tests:
    • Make sure your code works in isolation.
    • It's not a full code path.
    • He's purposely ignoring unit tests.
    • He encourages the confusion between unit tests and functional tests.
  • Functional tests:
    • Make sure your code works properly.
    • Use mock or live resources.
  • GUI tests:
    • Use a tool to record your interactions with an app and then play it back.
    • These are fragile.
  • Regression tests:
    • Making sure things don't get worse.
  • Acceptance tests:
    • "Unit tests ensure that you write the code right.
    • Acceptances tests ensure that you write the right code."
  • Mock testing:
    • Use "fake" resources so as to test your code with fewer dependencies.
    • Use mocking at the I/O boundaries.
  • nose:
    • You don't need to use the unittest API.
    • It's trivial. Write a test_foo.py module with a test_foo function. Run nose.
    • Unifies all the different test APIs.
    • Supports test fixtures via setup and teardown functions.
    • To test multiple apps: nosetests -w package0 -w package1 ...
    • If you have a lot of code, he recommends using nose from a Python script, not from the CLI.
    • The plugins are great.
  • Selenium:
    • This is GUI testing.
    • Test your AJAX.
    • Limited to a single Web site.
    • Really slick way to run tests in your browser.
    • You can script tests in Python.
    • Writing the scripts can be tedious, and they are fragile.
    • Useable for cross browser testing: Firefox, IE, Safari, Opera, etc.
    • Avoid it unless you're using AJAX.
  • My question: my tests pass, but I get bugs for cases I didn't consider:
    • You'll never:
      • Have complete code coverage.
      • Have tests for every situation.
      • Get away from the need for exploratory testing.
    • Automated tests free you up to do more exploratory testing.
    • When you find a bug, write test cases to try to flush out nearby bugs.
  • twill:
    • Speaker wrote it, and he likes it.
    • It's just a simple layer on top of other libraries.
    • Code in Python or "twill script".
    • In a sense, it is a scriptable browser, but it doesn't support JavaScript.
    • Run twill from within nose.
    • Can talk to WSGI directly.
    • It's lower level than Paste Fixture:
      • Unlike Paste Fixture, trivially toggle between direct WSGI or a live server.
  • figleaf:
    • A code coverage tool that's not restricted to just the CLI.
    • Code coverage is necessary, but not sufficient.
  • Continuous integration:
    • Continuous integration and buildbot are tremendously useful.
    • Distribute your building and testing across multiple platforms.
    • Tinderbox guys switched to buildbot.
    • For C and C++, he gave a plug for cmake.
    • You need to test in a cleanroom environment, on multiple platforms, in a developer neutral way.
    • Use a Subversion post commit hook to launch it.
  • Most important recommendations:
    • Start with some unit tests, some functional tests, and buildbot.
    • Build test fixtures as you need them, instead of ahead of time.
    • He's not a fan of test driven development.
      • This blew me away since he's foremost in the Python testing community.

Comments

Grig Gheorghiu said…
Shannon -- glad you found the tutorial useful! We'll put the slides online at some point, and add links to the tools we mentioned in the presentation.

Grig
Thanks, Grig.

Happy Hacking!
Krys said…
Hi Shannon,

I just wanted to say thanks for the great notes! :-) They helped me "get" the different types of tests a bit better.

I also decided to blog about your notes here.

Anyway, thanks again,
Krys
shday said…
Hi Shannon,

Your notes are enlightening. I've been using Selenium mostly because there are Firefox extensions that really help, like Selenium IDE. The IDE also allows you to test an app that hits multiple sites. I need this ability for what I'm doing.

Cheers,

Steve