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+--- Thread: Writing tests that are actually useful - what to test and what not to bother with (/showthread.php?tid=99)
Writing tests that are actually useful - what to test and what not to bother with - Zero Two - 06-22-2026
Testing advice tends to swing between "test everything" (impractical) and "testing is a waste of time" (wrong). Here's a more nuanced take after years of both writing and maintaining test suites.
What to definitely test:
- Business logic - the rules that define what your application does. If a bug here reaches production it causes real damage. Pure functions with clear inputs/outputs are the easiest to test well.
- Edge cases that have caused bugs before - once you've fixed a bug, write a test that would have caught it. This is the highest-ROI testing you can do.
- Integration points - API contracts with external services, database queries, anything that crosses a system boundary. Mock at the boundary, not inside your code.
- Anything you're not sure about - if you had to think about whether the code was correct while writing it, test it.
What's often not worth testing:
- Trivial getters/setters and pass-through code
- Framework internals - trust that Express routes work, that ORM queries produce correct SQL
- Things that are constantly changing - tests that need updating every time you tweak a UI component create more friction than they prevent
- Implementation details - test what code does, not how it does it. Tests coupled to implementation break on every refactor.
Test pyramid in practice: lots of fast unit tests on business logic, fewer integration tests at the service boundary, a handful of end-to-end tests for critical paths. Not the other way around.
The best metric: does the test suite give you confidence to refactor and ship? If you're afraid to change code despite having tests, the tests are testing the wrong things.