Why Test At All?

Tests are a safety net that let you change code without fear - this guide gives you the mental model that makes testing feel like a gift instead of a chore, before you write a single test.

1. Tests Are a Safety Net The real value of a test isn't catching bugs once - it's letting you change working code without fear, because a test will shout the moment you break something.
2. What a Test Actually Is A test is a small program that runs your real code with known inputs and asserts the result is what you expect - if the assertion fails, the test fails. Shown passing and failing.
3. What's Worth Testing (Straight Talk) Test the logic that matters, the bug you just fixed, and the tricky edge cases - don't chase 100% coverage of trivial code, and watch out for brittle tests and tests that test nothing.