Unit Testing in Java with JUnit 5 and Mockito

I used to hate writing tests. I thought it was a waste of time until I had to refactor a legacy module with 100% coupling. I broke everything, and I spent three days fixing bugs I introduced. That’s when I became a test convert. JUnit 5 is a joy to use compared to its predecessor. The `@ParameterizedTest` feature is a lifesaver when you need to test the same logic with 20 different inputs. And Mockito? It’s the best thing that happened to Java testing. Being able to mock external dependencies like databases or REST APIs allows you to test your business logic in isolation. The rule of thumb I follow: if your test requires a database connection, it’s an integration test, not a unit test. Keep them separate. Your build will run faster, and you’ll get faster feedback loops.