Nobody wakes up excited to write unit tests. But everyone's been woken up at 2am by a bug that tests would have caught. The goal isn't to love testing — it's to make it painless enough that you actually do it.
Why Tests Get Skipped
According to Martin Fowler's test pyramid, the most common reasons developers skip tests are: time pressure, unclear what to test, and the perception that tests slow down development. The irony is that skipping tests slows down development more — through debugging, regression bugs, and fear of refactoring.
What to Test (The Practical Version)
You don't need 100% code coverage. You need coverage on the code that matters:
- Business logic. Calculations, validations, state transitions. If it makes a decision, test it.
- Edge cases. Empty inputs, boundary values, null/undefined. These are where bugs hide.
- Integration points. API calls, database queries, file operations. Mock the external dependency, test your handling of responses.
- Bug fixes. Every bug you fix should get a test that would have caught it. Prevents regression.
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The Testing Pyramid
| Level | Speed | Coverage | When to Use |
|---|---|---|---|
| Unit tests | Milliseconds | Individual functions | Always. The foundation. |
| Integration tests | Seconds | Component interactions | API endpoints, DB queries |
| E2E tests | Minutes | Full user flows | Critical paths only (login, checkout) |
Most projects need lots of unit tests, some integration tests, and few E2E tests. The pyramid shape matters — inverting it (lots of E2E, few unit) leads to slow, flaky test suites.
Writing Tests That Don't Suck
- One assertion per test. If a test fails, you should know exactly what broke without reading the test code.
- Descriptive names. "test_calculate_tax_with_zero_income_returns_zero" not "test_tax_1".
- Arrange-Act-Assert. Set up the data, call the function, check the result. Three clear sections.
- No logic in tests. If your test has if/else or loops, it's too complex. Tests should be boring and obvious.
Related Tools
According to Google's engineering practices, tests are not optional — they're part of the code. A feature without tests is an unfinished feature.
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