How did you verify that developers' tests are actually working?

To verify that developer tests are truly working, you can:

• Run tests in an isolated environment: to ensure they pass and fail when code changes.
• Implement negative tests: intentionally introduce errors into the code and check that tests catch them.
• Check code coverage: using coverage tools to ensure tests cover key areas.
• Automate test runs in CI/CD: to see results with each commit.
• Analyze flakiness: identify unstable tests and eliminate causes of their failures.

For example, you can modify the function being tested to return an incorrect result and verify that the test fails, confirming its effectiveness.