Testing

A test that passes both before and after a change proves nothing. Builder writes the failing test first and keeps it as the evidence that the fix works.

Bug-fix protocol#

1. 1Reproduce the reported behaviour in a test. The test must fail on the current code.
2. 2Record the failure output as evidence in the trace.
3. 3Apply the minimal change.
4. 4Re-run: the new test passes and the existing suite stays green.
5. 5Report both runs side by side.

Test quality rules#

• Assert behaviour, not implementation detail. A test coupled to internals breaks on every refactor.
• Prefer one clear failure reason per test over a single test with twelve assertions.
• Cover the boundary and the error path, not only the success path.
• Do not mock the thing under test. Mocking the subject produces a test of the mock.
• Keep tests deterministic: no real clocks, no real network, no ordering dependence.