Interview with Harry Percival

If you develop and/or test web applications, especially django, you will probably enjoy this episode.

Show Notes

Rough outline of what we talk about:

Part 1 (first 20 minutes)

• Intro to Harry Percival, his background and story of how he got into TDD and ended up writing a book
• Hinting of perhaps a follow up tutorial to cover some more intermediate level topics.
• Testing django apps has some commonalities with testing flask, web2py, bottle, but djanogo does have some built in helpers.
• Comparing using unittest and pytest with applicability to testing django projects.
• Benefits of pytest treatment of asserts.
• Fixtures in pytest and how they seem magical. (and a reminder that pytest supports xUnit style setup/teardown).
• The meaning of “fixtures” as “data preparation” vs “setup/teardown”.
• Levels of testing, the test pyramid, end to end, functional, and unit testing.
• Some examples of very high level system testing using unittest and/or pytest.
• Where you put your tests in a django project and apps.
• Separating your functional testing from django app structure.
• Functional end to end testing with selenium.
• The django test client for middle level tests.
• Lower level test that perhaps don’t use django test client, or avoid the database.
• Business logic or algorithm tests might be candidates for isolated unit tests.

Part 2 (after the 20 minute mark)

• test isolation
  • testing a specific unit of code
  • perhaps only one function or method in isolation of rest of system
  • mocking or dependency injection
  • don’t have dependencies for a function
  • some logic examples where this work
• django and isolated unit tests
  • test isolation might not make sense for web applications
  • apps might be thin layers around a database
  • effort of isolation might not be worth it
  • django philosophy of “framework for perfectionists with deadlines”
  • view functions make a good place to test between the Internet and the models/database
  • larger projects might need testing at more levels, like around the business logic
• unit tests vs integration tests
  • bugs are in the interactions or interfaces or bad assumptions
  • revision control, history, and continuous integration services often help detect faulty code just as much as test isolation.
  • integration tests are often the most helpful because that’s often where the difficult to find failures occur.
  • pushing dependencies into fixtures can help with test isolation as well, by having dependency failures result in an Error and not a Failure.
  • Harry recommends a talk by Gary Bernhardt, Boundaries.
• Testing done by the development team without an external QA
• Double loop TDD: Functional test first, then unit tests
• Spikes: investigations without tests
• Harry’s experience with having a freely available web version of a book that is also intended to be sold.

Listen

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Links

• Test-Driven Development with Python – Harry’s book that I’m reading right now and highly recommend.
• Obey the Testing Goat – Harry’s site dedicated to the book and related posts.
• Python Testing with unittest, nose, pytest
• Support the show
• Gary Bernhardt’s talk, Boundaries talk including a discussion of “Functional Core, Imperative Shell”.
  • Above link is Gary’s site. Video is also on youtube
• Test-Driven Development with Python
• Support the show

Transcript

There is not a transcript available for this episode.
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