The answer to the question, is Unit testing.
Unit testing involves testing a site's program modules one at a time.
What is Unit testing?
Unit testing, often known as module or component testing, is a software testing technique in which individual program modules are tested to validate that each works correctly on its own. The objective of unit testing is to isolate a section of code and verify that the logic implemented works as expected.
What is the purpose of unit testing?
Unit testing is an important aspect of the software development process since it allows errors to be detected and corrected early in the development cycle. Unit testing is usually automated and can be done using a variety of testing frameworks. When a developer adds new functionality to an application, they should always create new unit tests to validate that the new code works as intended.