Testing
What to Test
Test behavior, not implementation. A test should verify what a function does, not how it does it. If you refactor the internals and the test breaks, the test was testing the wrong thing.
Good test: "given a valid email, returns true" Bad test: "calls regex.match with pattern /^[a-z].../"
Meaningful Coverage vs Line Coverage
100% line coverage is a vanity metric. You can have 100% coverage and still ship bugs if your tests don't exercise meaningful paths.
Focus
[Description truncada. Veja o README completo no GitHub.]