Verify the QUALITY of unit tests using code coverage and mutation testing, not just a green test run — then strengthen weak spots. Use this skill in any of three situations, even if the user does not mention coverage, mutation testing, or Stryker: (1) you just wrote or changed unit tests; (2) you are picking up an existing codebase and want to assess and improve its test suite; (3) you are reviewing a pull request or diff and need to judge whether its tests actually catch bugs. A passing test suite is never the finish line. For .NET projects, using coverlet for coverage and Stryker.NET for mutation testing.
