Test-driven development (TDD) is a software development process where the developer first writes a test for a new function, then writes the code to pass the test, and finally refactors the code. The steps in TDD are:

Write a Failing Test Case: Before any code is written, a test case is created to define the desired functionality.

Write Code to Pass the Test: The minimal amount of code necessary to pass the test is written.

Refactor: The code is refactored for optimization and improvement while ensuring that the tests still pass.