test-driven-development

Test-driven development prevents regressions by requiring a failing test to define expected behavior before writing production code. You verify the failure is correct, implement minimal code to pass, and run the full suite to ensure no regressions.

The red-green-refactor cycle enforces writing a failing test first, implementing the smallest code change to pass it, and cleaning up without adding new behavior. This verification-focused workflow ensures software quality throughout development.

To fix bugs without breaking existing features, reproduce the bug with a failing regression test first. Implement the fix to make the test pass, then run the full test suite to verify the bug is resolved and no regressions were introduced.

Yes, test-first development applies to refactoring by ensuring existing tests remain green after cleaning up code without adding new behavior. Run the full suite after modifications to verify no regressions occurred during the refactor.

Verifying a failing test fails for the correct reason prevents false positives from typos or import errors. Confirming the expected feature is missing ensures the subsequent minimal code implementation actually satisfies the desired behavior.

Test-driven development works with pytest by leveraging the testing framework to run failing tests, verify red states, implement minimal code to pass, and execute the full test suite for regression prevention across the workflow.