coverage

name	coverage
description	Check and increase test coverage to 100%. Use when coverage is below 100% or after writing new code. Identifies uncovered files, writes tests one file at a time, and repeats until fully covered.

Coverage Skill

You are tasked with bringing test coverage to 100%. Work through uncovered files one at a time until every file is fully covered.

Steps

1. Get a coverage overview. Run:

   mix coveralls
   

   Review the summary table. Identify all files below 100% coverage. If the user specified a file, start there — otherwise pick the file with the lowest coverage first.

2. Get detailed coverage for the target file. Run:

   mix coveralls.detail --filter <filename_without_extension>
   

   This shows line-by-line coverage. Note which lines are marked as missed.

3. Read the source file to understand the uncovered code paths — what conditions, branches, or error cases are not tested.

4. Read the existing test file (if one exists) for context on patterns, fixtures, and helpers already in use.

5. Write tests to cover the missing lines:

   • Follow existing test patterns in the file (describe blocks grouped by function, fixtures, etc.)
   • Use the project's testing conventions from CLAUDE.md (Mimic for mocking, fixtures in test/support/fixtures/)
   • Focus on exercising the specific uncovered branches/conditions
   • Don't add redundant tests for already-covered code

6. Verify coverage improved by re-running:

   mix coveralls.detail --filter <filename_without_extension>
   

   If the file is not yet at 100%, go back to step 3 and cover the remaining lines.

7. Once the file reaches 100%, move to the next uncovered file. Repeat steps 2–6 for each file until all files are at 100%.

8. Run the full check to make sure nothing is broken:

   make
   

Important Notes

• Always use mix coveralls commands (not mix test --cover) — this project uses ExCoveralls.
• Work one file at a time. Don't try to cover everything at once.
• If a file is at 100% already, skip it and move on.
• When writing tests, keep them focused and minimal — cover the missed lines without over-testing.
• Never use # coveralls-ignore-start / # coveralls-ignore-end to skip lines. If code appears unreachable, ask why it exists — if code is so defensive that it can't be tested, it should be removed, not hidden. Use coveralls.json skip_files only for generated or infrastructure files already listed there.