Sleeping instead of synchronizing
Do not usetime.Sleep to wait for async work. Use require.Eventually or a test clock.
Testing implementation details
Verify public behavior, not internal fields. Refactors should not break tests when behavior is unchanged.Shared mutable state
Avoid global state between tests. Isolate resources per test or reset state explicitly.Ignoring setup errors
Fail fast on setup errors so failures are clear and localized.Hardcoded identifiers
Usepkg/uid to generate unique IDs so parallel tests do not collide.
Over-mocking
Prefer real dependencies when feasible. Mocks often assert calls instead of behavior.Missing subtests
Uset.Run for table cases so failures identify the case.
Forgetting t.Helper()
Helpers that assert must call t.Helper() so failures point at the call site.