Test-driven development(TDD) is a software development methodology where developers write tests before writing code.

The process begins by writing a test that defines the desired behavior of the system.

The test is then run, and it should fail because there is no code to implement the desired behavior.

The developer then writes the minimum amount of code required to make the test pass.

The test is then run again, and it should pass.

TDD emphasizes writing automated tests as a means of improving the quality of the code and ensuring that it behaves as expected.

TDD can also improve code maintainability by making it easier to add new features, fix bugs, and modify existing code.

TDD is often used in conjunction with agile software development methodologies such as Scrum.