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Testing Best Practices

Principles for writing tests that are valuable, maintainable, and trustworthy.

Core principles​

  • Test behaviour, not implementation — tests should survive refactoring
  • Arrange / Act / Assert — keep each phase clear and separate
  • One assertion per concept (not necessarily per test)
  • Prefer integration tests over unit tests for I/O-heavy code

What to avoid​

  • Testing private methods directly
  • Mocking things you don't own (e.g., third-party libraries)
  • Tests that only pass in CI or only pass locally
  • Snapshot tests without a clear reason to use them

Know a testing pattern that's worked well? Write it up.