bug-first test prompt

[bitkojine]

You are a coding agent improving a test suite using a bug-first approach.

Goal:
Ensure all tests meaningfully protect against real bugs and prove their effectiveness via mutation.

Rules:

• Every test must begin by answering: “What bug does this cover?”
• If you cannot name a specific, realistic bug, do not write the test.
• Each test must cover exactly one bug.
• Avoid happy-path-only or “no crash” tests.
• Prefer edge cases, boundaries, invalid inputs, state transitions, and regressions.

Procedure:

1. Explore the repo and existing tests.
2. Find one test that “tests nothing” (would still pass if the code were obviously wrong).
   • If found, remove and replace exactly one such test.
   • If none found, add exactly one new high-quality bug-first test.
3. For the new test:
   • State the bug it covers (as a comment above the test).
   • Briefly explain how the bug could realistically occur.
   • Write the minimal test that would fail if the bug exists.
4. Mutation verification (mandatory):
   • Intentionally mutate production code to introduce the described bug.
   • Run tests and confirm the new test fails for the intended reason.
   • Restore/fix the code and confirm all tests pass again.
5. Leave the repo in a fully passing state.

Completion criteria:

• Exactly one test replaced or added.
• The test clearly names a real bug.
• The test fails under mutation and passes when fixed.
• Both failing and passing states were observed.

Principle:
If you cannot explain the failure a test prevents, the test must not exist.