A github action that generates a comprehensive unit test coverage report, including optional diff with the branch the PR will merge into.

- uses: jgillick/test-coverage-reporter@v1
  with:
    coverage-file: coverage/coverage-final.json
    access-token: ${{ secrets.GITHUB_TOKEN }}

• coverage-file: Path to the test coverage report
• base-coverage-file: Path to the coverage report to compare against. This is most likely from the branch you plan to merge into.
• access-token: Required to comment on the PR
• title: The coverage report title
• strip-path-prefix: Remove this part of the path of the front of all file paths in the coverage report.
• fail-file-reduced: If coverage for any file is reduced by this much (in percent) the run will fail. (default: 0.2)
• custom-message: Add this custom text to the output.

You can easily see how this PR will either add or remove coverage from the branch it will merge into by passing the base-coverage-file input.

report:
  permissions: write-all
  ...
  steps:
    ...
    
    - name: Generate report
      uses: jgillick/test-coverage-reporter@v1
      with:
        coverage-file: coverage/coverage-final.json
        base-coverage-file: main-branch/coverage/coverage-final.json
        access-token: ${{ secrets.GITHUB_TOKEN }}

See a full example in this repos workflow.

For larger test suites, it can be more performant to save the base coverage to a longer-lived artifact and use an action like actions-download-artifact to download it.

You might also like the Test Coverage Annotations action, which makes it easier to see which lines are lacking test coverage.

This action was inspired by the work of Jest coverage report and Jest Coverage Reporter Action.