Test-driven development (TDD) is about writing automated tests that verify whether the code actually works. TDD focuses on development with well-defined requirements in the form of tests. Every development process includes testing either in an automated or manual way. Automated tests result in an overall faster development cycle. Efficient TDD is faster than development without tests. Comprehensive test coverage provides confidence in the application development and this confidence enables refactoring for the application. Refactoring is essential to the agile development of an application. Let's see the following diagram:

Refactoring promotes agile development; it is easy to discover failures and it fixes them.

Testing makes you think about your design. If your code is hard to test, then the design should be reconsidered. A test case helps you focus on what matters. It helps you not to write code that you don't need and it finds problems early during development. Let's see the different types testing in software.