tdd

Test-driven development begins by writing a failing test that defines the expected behavior before any implementation. You then write minimal code to pass the test, expand coverage to error paths, and refactor safely while maintaining strict red-green-refactor sequencing.

Negative-space testing requires explicit assertions for error paths, boundaries, and untrusted input vectors rather than just happy paths. It is essential for regression coverage because it validates system behavior across unit and integration boundaries where failures commonly originate.

To eliminate flaky tests during refactoring, apply failure-focused run rules that enforce non-destructive test isolation and proper failure interpretation. Avoid over-mocking by relying on observable behavior verification through inversion-of-control and state-access reviews.

A testability audit is an inversion-of-control and state-access review that ensures code can be verified through observable behavior. You should perform one before writing tests to guarantee your architecture supports reliable behavioral contracts and reduces flakiness.

Test-driven development is effective for fixing bugs and regressions because it enforces a contract-first workflow where precise test coverage anchors correctness. You write a failing test reproducing the regression, implement the fix, and verify behavior across boundaries.

Test suites break during refactoring when tests lack behavioral contracts or depend on implementation details rather than observable behavior. Following strict red-green-refactor sequencing and performing testability audits beforehand anchors correctness and prevents fragile failures.