Testing Best Practices
Good tests do more than verify code works — they serve as documentation, catch regressions, and give you confidence to change things. But poorly written tests become a maintenance burden that slows development. Learning best practices helps you write tests that provide lasting value.
The Testing Pyramid
Not all tests are equal. The testing pyramid guides how many of each type to write:
/\ E2E: Few, critical user flows
/ \
/ \ Integration: Important component interactions
/ \
/ \ Unit: Many, fast, isolated tests
/__________\
Unit tests form the foundation — they're fast, focused, and catch most bugs. Integration tests verify components work together. End-to-end tests are expensive but validate critical user journeys.
Writing Maintainable Tests
Use descriptive names: Test names should explain what's being tested and expected outcome.
# Bad
def test_user():
...
# Good
def test_user_creation_fails_with_invalid_email():
...
Test behavior, not implementation: Tests should verify what code does, not how it does it. If you refactor internals, tests shouldn't break.
Keep tests independent: Each test should set up its own state and clean up after itself. Tests that depend on each other create debugging nightmares.
Clean up test data: Don't leave database records or files lying around. Use setup and teardown methods or test fixtures.
Anti-Patterns to Avoid
Testing implementation details: If your test breaks when you rename a private method, it's testing the wrong thing.
Flaky tests: Tests that sometimes pass and sometimes fail destroy trust in your test suite. Fix or delete them immediately.
Slow test suites: If tests take too long, developers stop running them. Keep unit tests fast — milliseconds, not seconds.
Over-mocking: When you mock everything, your test proves nothing about real behavior. Mock external dependencies, not your own code.
# Too much mocking - test proves nothing
def test_process_order(mock_validator, mock_calculator, mock_db):
mock_validator.return_value = True
mock_calculator.return_value = 100
# What are we even testing?
Balance Coverage With Value
100% code coverage sounds good but isn't always practical or valuable. Focus coverage on critical paths and complex logic. Simple getters and setters rarely need dedicated tests.