Test-Driven Development (TDD)

3/27/2022 6:30 PM: -- Test-Driven Development (TDD) is a software development approach that emphasizes the importance of writing automated tests before writing any production code. Unit testing, on the other hand, is primarily focused on testing individual units of code to ensure they are functioning correctly. While unit testing is an important aspect of software development, it is not the same as TDD. Unit testing is about testing, while TDD is about design.

In TDD, developers should begin by writing a test for a piece of functionality before writing the code will be tested. Initially the test should fail. A test is written for code that does not exist yet. It may not even compile at this point which counts as a failure. Once the test is written, the minimal amount of code necessary is written to make the test pass. As each test is written and the corresponding code is written which makes the test pass, the design of the code takes shape, with each test building on the last.

It's even common to hard-code the expected result to make the test pass. Once the test is passing, the next step is to refactor the code. The goal is to replace the hard-coded values with the actual logic that should be implemented in small, incremental steps, and each step is verified by running the tests again. By doing so, the developer can be sure that he is not breaking any existing functionality. This is the iterative process that is repeated many times during the development cycle. Make progress in small, manageable steps adding functionality incrementally. As tests are written and run, one gets a sense of whether their code is working as expected, which can help them identify and fix problems early on.

Refactoring is a primary driver of the design process. As the design takes shape, you review the code and make changes to improve its structure and quality. As the design becomes more complex, it might become necessary to re-write or throw away tests. The design and requirements of the project may change as the design evolves.

Tests are not just a way to check that the code is working, but they also serve as a specification of the desired behavior.

The TDD approach should lead to better design and fewer bugs. It allows developers to focus on one piece of functionality at a time, rather than trying to implement everything at once. Verifying that the code is working correctly after each change without breaking code or introducing bugs. It encourages developers to write the minimum amount of code necessary to meet the requirements of the software design.