Introduction to test-driven development (TDD)

- [Instructor] Before I explain what Test Driven Development is, first, you should know that Tests or Test Cases are simply software requirements and specifications derived from Use Cases and User Stories. Test Driven Development, TDD, is a software development process relying on software requirements being converted to test cases before software is fully developed and tracking software development by repeatedly testing the software against all test cases, as opposed to software being developed first and test cases created later. Test Driven Development is also called Test First Development because you first write a test before you write just enough production code to fulfill that test and then go on to refactor the production code. Let's talk about the life cycle of Test Driven Development. It spins around five steps, which are repeated continuously all through the agile methodology in software development. The first step is to write the test. In Test Driven Development, the adding of a new feature begins by writing a test that passes if the feature's specifications are met. This is in contrast with the usual practice where unit tests are only written after code. For the second step, you affirm the test fails. Run all tests. The new test should fail. This is to validate that the test is working correctly and new code is needed for the desired feature. In the third step, you will write code to pass the test. Write the simplest code that passes the new test. Inelegance code is acceptable as long as it passes the test. The code will be refactored in step five. You should not write code beyond the tested functionality. For the fourth step, you will affirm the test passes. Run all tests. They should all now pass. If any fails, the new code must be revisited until they pass because the new code must meet the test requirements and not break existing features. Step five is Refactor. Remove hard-coded test data and refactor as needed for readability and maintainability, running tests after each refactor to ensure that functionality is preserved. Finally, we will repeat this cycle for each new piece of functionality. Tests should be small and incremental and commits made often. That way, if new code fails some tests you can simply undo or revert rather than debug excessively. Test Driven Development makes you focus on requirements before writing code. And some of its benefits include improved code quality, detailed project documentation, safe project costs in the long run, and bugs are reduced. There are three major types of Test Driven Development. Namely, Unit Tests, Integration Tests, and End to End Tests. In the coming videos, we will discuss each of these types of TDD in detail.