test-driven-development

Test-driven development prevents regressions by enforcing a fail-first discipline, ensuring new features and bug fixes are built exclusively on failing tests before any production code is written.

The red-green-refactor cycle in unit testing is a development process where you write a failing test first, implement the minimal production code to satisfy it, and then refactor the code for clarity.

To apply TDD when refactoring, you must write explicit failing tests covering critical behavior first, then modify the code to pass those tests, ensuring no production code changes occur without a failing test.

You need a testing framework like pytest or an equivalent environment to practice strict TDD, supported by a policy that no production code is written without a failing test first.

You should reconsider a fail-first development process if your project lacks a testing framework or cannot enforce the policy requiring explicit test coverage for critical behavior before writing code.