What is test-driven development (TDD)?

Test-driven development (TDD) is a software development approach that prioritizes writing tests before any actual coding takes place. This method is characterized by a cycle that begins with writing a test that defines a desired function or improvement, and then developing the minimal code required to pass that test. Once the code passes, the developer may refactor it while ensuring that the tests still pass, thereby maintaining code quality.

The significance of this approach lies in its emphasis on the concept of "failing fast." By establishing tests upfront, developers can ensure that each new piece of code they create meets the design requirements and functions correctly from the outset. This reduces the likelihood of introducing defects and encourages better design decisions, as the tests often enforce separation of concerns and better abstraction.

The result is a more reliable codebase that can be modified over time without fear of breaking existing functionality because the tests provide immediate feedback. TDD also fosters greater collaboration among team members, as it clarifies expectations and requirements through the lens of tests.

In contrast, other choices represent different philosophies or misunderstandings about the software development process. For instance, the idea that coding should be done first runs counter to the defining principle of TDD, while suggesting that testing can be eliminated overlooks the essential role