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Test-driven development writes failing tests first, then minimal implementation to pass them. This approach ensures code changes are validated by tests before committing, using red-green-refactor cycles where tests are written prior to implementation across feature development, bug fixes, and refactors.

Atomic commits capture one complete red-green-refactor cycle—a failing test, minimal code to pass it, and any refactoring. Each commit should have a clear, descriptive message that reflects the specific task completed, enabling reviewers to understand the progression of changes.

Real tests include specific assertions that verify expected outcomes and edge cases, not just confirm code runs without errors. Tests should validate actual behavior—return values, state changes, error conditions—ensuring they catch regressions and document requirements.

TDD applies to feature development, bug fixes, and refactors across any codebase. Start by writing a failing test for the specific change, implement minimally to pass it, then commit atomically. Existing code can adopt TDD incrementally, one task at a time.

Debugging mode treats test failures as design feedback. Review the failing test to confirm it captures the intended behavior, adjust either the test or implementation, then re-run. The test should always guide the implementation, not the reverse.

Basic testing framework knowledge helps but isn't required to begin. TDD principles—write failing test, implement minimally, refactor, commit—work with any testing tool. Start simple with assertions and edge cases, then deepen framework expertise as needed.