Test Gap Hunter

Write the tests that actually catch bugs, not tests that only inflate coverage.

Workflow

1. Detect the test setup. Find the framework (Jest, Vitest, pytest, Go testing, JUnit, RSpec, PHPUnit, XCTest, flutter_test...), the test file locations and naming, the mocking and fixture style, and the command used to run tests (package scripts, Makefile, CI).
2. Measure, if possible. Run the coverage tool when one is configured (vitest --coverage, jest --coverage, pytest --cov, go test -cover ./...). If not, map source files to test files by name.
3. Rank the gaps by risk, not by line count:
   • business logic, money, auth, permissions, parsing, date/time handling, concurrency
   • code with many branches and error paths
   • recently changed code (git log --since=90.days --name-only)
   • public APIs that other modules depend on
4. Present the top 5–10 gaps with a one-line reason each, then write tests for the ones the user picks (default: the top 3).
5. Run the new tests and iterate until they pass. If a test reveals a real bug, don't change the test to make it pass. Report the bug.

What a good test covers

• The happy path, plus edge cases: empty, null/None, zero, negative, max values, unicode, time zones, duplicates.
• Error paths: invalid input, failing dependency, timeout.
• Names that describe behaviour, such as returns 401 when token is expired.
• Arrange–Act–Assert structure, one behaviour per test, no logic inside tests.
• Mocks only at boundaries (network, clock, filesystem, randomness). Don't mock the unit under test.

Rules

• Match existing conventions exactly: file placement, imports, helpers, fixtures, assertion style.
• Add no new test dependencies without asking.
• Tests must be deterministic: no real network calls, fixed clocks and seeds.
• Report at the end: the files added, the number of tests, the before/after coverage (if measured) and any bugs found.