| name | test-backfill |
| description | Fill test coverage gaps to hit the project's target (AGENTS.md says ≥80% on src/). Reads existing tests to match style, prioritizes public-API and error paths, runs the suite after every batch. |
Test Backfill
Raise coverage without shipping bad tests.
Process
- Read existing tests. Learn the framework, assertion style, fixture patterns, naming convention. Never introduce a second style.
- Run coverage. Capture the report. Identify the gaps.
- Prioritize, in order:
- Public API surface (exported functions, HTTP endpoints, CLI commands)
- Error paths (throws, rejections, non-200s, invariant violations)
- Edge cases (null, empty, boundary, concurrent)
- Happy path (least valuable — usually already tested)
- UI details (lowest priority, hardest to maintain)
- Write tests in batches of 5–10. Run the suite after each batch.
- If a batch fails, stop and investigate before writing more.
- Every new function gets at least one failure-path test.
- Hand off coverage numbers at the end: "coverage now X%, was Y%, Δ = +Z pp".
Quality Bar
A good test:
- Tests behaviour, not implementation.
- Reads like a specification: "when X, the function does Y".
- Has one assertion per logical check (but may have multiple physical assertions).
- Runs in < 100 ms unless it's explicitly an integration test.
- Is deterministic. No wall-clock, no network, no RNG — or inject them.
A bad test:
- Tests internal state / private methods directly.
- Mocks so much of the system under test that it's not really testing anything.
- Depends on test execution order.
- Has "magic" fixture values with no explanation.
- Uses
try/catch instead of expect().toThrow() (or equivalent).
Anti-Patterns to Kill
- Tests that always pass (e.g.,
expect(true).toBe(true) stubs)
- Tests with no assertions (function runs, nothing's checked)
- Tests that catch all exceptions silently
sleep(N) — use a proper wait-for-condition utility- Tests that talk to the real network or real database without a
@integration tag
Never
- Modify production code to make a test easier, beyond adding a dependency-injection seam.
- Weaken an assertion to green a test.
- Mark a test
.skip without a dated TODO and an owner.
- Copy-paste a test and flip one value without asking "is this actually a different case?"
- Inflate coverage with meaningless tests. 78% with real tests > 85% with theater.
