| name | write-test |
| description | Write a test to improve code coverage. Uses `cargo llvm-cov` to identify uncovered lines, then writes a focused test to cover them. Use when user says "write test", "improve coverage", "cover lines", or "write-test". |
Write Test (Coverage-Guided)
Write a single focused test to improve code coverage, guided by cargo llvm-cov output.
Instructions
Step 1: Identify uncovered lines
If the user specified a target file, run:
just uncovered <file>
If no file was specified, run just uncovered to see all uncovered lines, then pick the highest-impact target (most uncovered lines or most important code path).
IMPORTANT: After the initial scan, always scope just uncovered to the target file to keep context small.
Step 2: Read the source
Read the target file to understand what the uncovered lines do. Focus on understanding the code paths that lead to those lines — what inputs, configurations, or conditions trigger them.
Step 3: Write one test
Write a single focused test that exercises the uncovered code path. Place it in the appropriate test module or file following existing project conventions.
Only write one test per invocation. Keep it minimal and targeted at the specific uncovered lines.
Step 4: Verify improvement
Run coverage again and compare:
just uncovered <file>
Compare the before and after just uncovered output. Confirm that previously uncovered lines are now covered. If the test didn't improve coverage as expected, investigate why and adjust.
Notes
- The
just uncovered output is compact (one line per file with collapsed ranges) to minimize token usage. Prefer it over reading raw lcov.info.
- If a line remains uncovered after your test, it may be dead code, error handling for impossible states, or require more complex setup. Note this to the user rather than forcing coverage.
