How did you create tests for individual system components?

To create tests for individual system components, I used unit testing. Usually, I would isolate a specific component or class and write tests for it that checked its behavior in isolation from the rest of the system. This allowed for quick error detection and ensured that code changes did not break functionality.

For example, to test a function, I would create a set of input data and verify that the output matched the expected result. For components with external dependencies, I used mock objects to isolate the code under test.

The tools I used include JUnit for Java, NUnit for C#, and Jest for JavaScript. It is important that the tests are automated and run with every code change.