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cs4140 Notes: 21 Test Driven Development

··2 mins

Test-Driven Development

Workflow for adding code:

  • We have a story on our Kanban board, marked “in progress”.
    • What needs to be done is clearly defined.
    • Acceptance criteria for manual testing is defined.
  • Create feature branch.
  • Write code and tests.
  • Make pull request.
  • Code review.
  • Deployed automatically.

Focusing in on the code writing step, we’ve got a process question: Should the functional code get written first, or the tests?

The Test Driven Development philosophy says write a test first. Why?

  • The feature needs to be very clearly defined.
  • You can’t add features without first figuring out how to test them.
  • This sequence incentivizes writing the simplest code that will pass the test.

More specifically, the sequence goes like this:

  • Write one new test.
  • Run the test suite and confirm that the new test fails.
  • Make the minimum change nessisary to pass the test.
  • Run the test suite and confirm that the new test passes and no other tests break.
  • Do any refactoring needed to clean up this specific functionality, making sure that all tests stay passing.

Let’s see this in action:

  • Add a feature to Next app. (npx run jest)
  • Add a feature to Rails app. (rake test)

Test coverage

Test Coverage for Rails

Test Coverage for Next

Now let’s extend coverage to everything in app.

In jest.config.mjs:

const config = {
  ...
  collectCoverageFrom: [
    'app/**/*.{js,jsx}'
  ]

Now let’s check the report:

xdg-open coverage/lcov-report/index.html
  • Find code that isn’t covered, write test.

Other refs:

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