Proof

An edit is not finished when it compiles. It is finished when it can be shown to work: tests pass, the failing case is covered, and the behavior is visible in the running application. Proof is what separates a change from a guess.

Run the test suite before and after. The before tells you the baseline; the after tells you the cost of your change. When a task is about a specific failure, write a test that reproduces it first, then make it pass. A regression that cannot be reproduced cannot be proven fixed.

For interface work, browser evidence is the proof. Load the page, exercise the interaction, and confirm the state the user actually sees. Screenshots and console output are the receipts of that verification.

If something cannot be verified, say so. An honest “I could not test X because Y” is worth more than a silent assumption. Proof includes knowing the limits of your own evidence.