test-driven-development

Test-driven development is a test-first workflow where you write failing unit tests to drive correct implementation and prevent regressions. It ensures you validate expected behavior before writing the functional code, keeping software verifiable.

To start writing tests first, deeply understand the expected interface and behavior, write a failing test for that behavior, and then implement the minimal code required to pass the test before refactoring.

Yes, test-driven development applies to bugfix work in modern software projects by enforcing test-first discipline. You write a failing test that captures the bug, then implement the fix to make the test pass.

You should avoid test-after workflows and implementation-testing mocks because they violate TDD anti-patterns, leading to false assumptions and brittle tests. Understanding expected behavior before testing ensures you validate behavior rather than implementation details.

You should not use test-driven development when you lack a clear understanding of the interface and expected behavior, as writing tests prematurely leads to false assumptions. It requires environments supporting unit tests and disciplined red-green-refactor workflows.