| name | test-writer |
| description | Use to add or update tests using the existing test framework for changed behavior, edge cases, regressions, or existing untested code the user wants covered. |
| allowed-tools | Read, Grep, Glob, Bash, Edit, Write |
| when_to_use | Use automatically when behavior changes, or manually when the user asks for tests — including adding coverage to existing untested/legacy code with no behavior change. |
| argument-hint | [file or function to test] |
| context | fork |
| agent | senior-engineer |
| effort | medium |
test-writer
Fires for backend service/controller/repo/handler/use-case, mobile ViewModel/UseCase/Repository, frontend server action/API route. Not for pure UI changes.
Process
- Read budget: changed file + existing test file (
*.spec.ts / *_test.go / test_*.py) — 2 files max.
- Write 3-6 cases, one assertion each: happy path (1) + edge/boundary (1-2) + error (1) + regression if bugfix (1).
- Mock: external HTTP APIs, email/payment gateways, external SDKs, Date.now(), Math.random(). Never mock internal pure functions, utility functions, type mappers, constants, or your own DB (use a test DB — see
rules/300-testing.md).
- Run targeted only:
jest [file].spec.ts --no-coverage | vitest run [file] | go test ./pkg/... -run TestFn | pytest [file] -x -q | ./gradlew test --tests "*.Class"
Output
TEST: [test names] | FILE: [path] | RUN: [command — ✓ N passed] | MOCKS: [list | none]
