In test-driven development (TDD), when are tests written?

In test-driven development (TDD), tests are formulated before writing the actual code. This approach is foundational to TDD, as it emphasizes the creation of test cases that define desired functionalities before any implementation takes place. By writing tests first, developers ensure that their code is specifically tailored to meet outlined requirements and that it passes these tests.

This method fosters better program design, encourages simpler code, and highlights any misunderstandings regarding requirements early in the development process. As tests are created based on the expected behavior, they guide the coding efforts and help already in the planning stages, thereby reducing the likelihood of defects and the need for extensive debugging later.

The focus on testing from the outset also enhances maintainability, as comprehensive test suites are built up over time, ensuring that modifications can be made with confidence, knowing that existing functionality will be preserved.