In what is TDD, you always begin with the most important behavior the user or system needs. The TDD approach says: write a test for a small, clear requirement before writing any code. When understanding what is test driven development, the key idea is to start with tests that describe what the code should do, not how it does it. In TDD development, write the first test for the simplest and most critical case, then move step by step to edge cases and validations. This order keeps development focused and avoids unnecessary code. One of the main benefits of TDD is that it gives quick feedback and keeps the design clean. The long-term advantages of test driven development include fewer bugs, easier changes, and more confidence while refactoring. Conclusion: In TDD, always write tests first for the core behavior, keep them small, and grow functionality gradually. This ensures clear requirements, stable code, and maximum value from test-driven development.