Which of the following describes a proper use case for test-driven development?

Test-driven development (TDD) emphasizes the practice of writing tests before implementing the actual code. This approach encourages developers to clearly define the desired behavior of a piece of software before it is built, which helps ensure that the code meets its specifications right from the start. By writing tests first, developers create a sort of blueprint for their code, which guides the implementation and allows for immediate verification of that implementation as it proceeds.

This proactive method cultivates a coding discipline where developers are continuously thinking about how their code functions and how it should be tested. It leads to more modular, maintainable code, as each piece is developed and validated iteratively through a cycle of writing a test, implementing the feature, and refactoring as necessary. In contrast, writing tests after the code is complete, implementing code that doesn’t require testing, or revising existing code without establishing tests does not align with the core principles of TDD. These practices can lead to less reliable code and make it more difficult to catch defects early in the development process.