What is 'test-driven development' (TDD)?

Test-driven development (TDD) is a software development approach where tests are written before the actual code is implemented. This practice emphasizes the importance of defining the desired behavior of a program through tests prior to writing the code that fulfills those requirements. The typical cycle in TDD involves writing a test for a specific feature or functionality, running the test to see it fail (since the feature has not yet been implemented), and then writing the minimal amount of code necessary to make that test pass. This iterative process continues with refactoring the code as needed while ensuring that all tests remain successful.

The core aim of TDD is to create a robust design and enhance confidence that new changes or features do not break existing functionality, leading to higher quality software. This methodology fosters a clear understanding of how the software should behave from the outset, helping developers avoid missteps that can occur when writing code without predefined tests.