What is test-driven development (TDD) and how does it work?

Test-driven development (TDD) is a software development approach that emphasizes writing tests before writing the actual code. It follows a cycle of writing a failing test, writing the minimum amount of code to pass the test, and then refactoring the code to improve its design and maintainability.

The TDD process typically involves the following steps:

1. Write a test: The developer starts by writing a test case that defines the desired behavior of a specific piece of code. This test is expected to fail initially since the code being tested does not exist yet.

2. Run the test: The developer runs all the existing tests, including the newly written one. Since the code is not implemented yet, the test will fail as expected.

3. Write the code: The developer then writes the minimum amount of code required to pass the failing test. The focus is on making the test pass, rather than writing the entire functionality at once.

4. Run the tests again: After writing the code, the developer runs all the tests again, including the new one. If the test passes, it indicates that the code meets the desired behavior defined by the test. If any test fails, it means that the code implementation is incorrect or incomplete.

5. Refactor the code: Once the test passes, the developer refactors the code to improve its design, readability, and maintainability. This step ensures that the code remains clean and efficient while still passing all the tests.

6. Repeat the cycle: The developer repeats this cycle by writing another failing test for the next desired functionality, writing the code to pass the test, running the tests, and refactoring the code. This iterative process continues until all the desired functionality is implemented.

The key benefits of TDD include improved code quality, faster feedback on code changes, increased test coverage, and better maintainability. By writing tests first, TDD helps developers to think about the desired behavior and design of the code before implementation, leading to more reliable and robust software.