test-driven-development

To start writing unit tests before implementation, write a failing test that captures the specific behavior requirement, confirm it fails, then add only enough production code to make it pass.

The red-green-refactor workflow requires writing a failing test first to prove the requirement, implementing minimal code to pass it, and then refactoring safely while maintaining regression protection.

To prevent regression when fixing bugs, write a failing unit test that reproduces the specific bug, implement the fix to turn the test green, and keep the test as a repeatable regression guard.

You need real-behavior tests when validating actual code paths to ensure deterministic verification, avoiding test-only shortcuts or mock behavior that might hide integration failures.

Yes, you can apply test-driven development to refactoring by writing failing tests that lock in current interface changes and behavior, ensuring your structural modifications have strict regression protection.

The best way to enforce fail-first discipline is to prevent production code from being written until a failing test proves the requirement, requiring strict verification that each test fails before code is added.