| name | acp-test-first |
| description | Use when the user asks to fix a bug, add behavior, or change behavior in a project that has a test framework, AND the change can be expressed as an observable input/output contract. Writes a failing test first, then makes the smallest change to pass it. |
| version | 1.0.0 |
Test First Skill
Use this skill when the user asks to fix a bug, add behavior, or make a change that can be verified through tests.
The goal is to let tests describe the expected behavior before implementation details are changed.
When to Use
Use this skill for:
- Bug fixes.
- Behavior changes.
- Edge case handling.
- Regression prevention.
- Refactors that need safety coverage.
Do not force test-first work when the project has no test framework or when the task is purely exploratory. In that case, document the missing test environment.
Workflow
1. Define Expected Behavior
Before writing code, write down:
- What should happen?
- What currently happens?
- What input triggers the behavior?
- What output, state, or side effect should be observed?
2. Write or Identify a Failing Test
Prefer a test that fails for the right reason.
A good failing test is:
- Focused.
- Easy to understand.
- Related to the user request.
- Not coupled to unnecessary implementation details.
Avoid tests that only verify that a mocked internal function was called unless that is the actual contract.
3. Make the Smallest Implementation Change
Change only the code needed to make the test pass.
Do not:
- Rewrite nearby code.
- Add generic abstractions.
- Change public APIs unless required.
- Add unrelated test cases in the same step.
4. Run the Test Again
After implementation:
- Run the new or changed test.
- Run related tests.
- Run typecheck, lint, or build if available.
If checks cannot be run, say so clearly.
Output Format
Expected behavior:
- ...
Failing test:
- ...
Implementation:
- ...
Verified:
- ...
Not verified:
- ...
Guardrail
Do not change the test just to match a wrong implementation.
If the test reveals that the requirement is ambiguous or wrong, stop and ask for clarification.
