Assumptions are continually verified. We refactor the code (change the internal structure of the code without affecting the output of the system) to improve code quality such as maintainability, readability, or extensibility. We can refactor the code with confidence if automated unit tests are running and providing feedback.

Side effects are detected immediately. This is useful for fragile, tightly coupled systems when a change in one module breaks another module.

Test automation saves time and there is no need of immediate regression testing. Suppose you are adding a scientific computation behavior to an existing calculator program and modifying the code. After every piece of change, you perform regression testing to verify the integrity...