work-tdd

Write one failing test describing the desired behaviour, run it to confirm it fails for the right reason, write the minimal code to pass it, then refactor while all tests stay green. Repeat the cycle for each new piece of behaviour.

Red means writing a failing test, green means writing the simplest code that makes it pass, and refactor means cleaning up duplication and names while every test remains passing. No new behaviour is added during refactoring.

A test passing on its first run means it exercises behaviour that already exists or tests nothing real. Fix the test so it genuinely fails, or stash existing production code and watch the failure before restoring it.

Mocks belong only at true system boundaries. Before mocking, identify the real method's side effects, check whether the test depends on them, and mock at a lower level that preserves required behaviour.

Methods used only by tests pollute the production API and hide design problems. Move cleanup or setup logic into dedicated test utilities instead of extending production classes.