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Red → Green (tests fail BEFORE the fix)

description: “Red → Green: for non-trivial features and bugfixes, write the tests first, run them and watch them FAIL, then write the smallest fix that turns them green.” alwaysApply: true

Section titled “description: “Red → Green: for non-trivial features and bugfixes, write the tests first, run them and watch them FAIL, then write the smallest fix that turns them green.” alwaysApply: true”

For non-trivial features and bugfixes, brief your implementers to write the tests first, run them and watch them fail (Red), then write the fix and watch them turn Green.

  1. A BDD / integration test that exercises the user-facing behavior through the real harness — its job is to fail before the fix and pass after.
  2. Unit tests pinning every branch of any new logic the fix introduces.
  3. Run them — they MUST fail. Record the failure output. A test that passes before the fix is testing the wrong thing; rewrite it until it fails for the right reason.
  4. Then implement the smallest change that turns both layers green.

The Red step is non-negotiable: “wrote the test and the fix together and they pass” is not Red → Green. Reproduce the reported failure shape verbatim — do not encode the answer into the setup, or the test goes green while the real broken path is never exercised. Both states must be observable: “before: N failures, after: 0.”