JUnit Testing

The previous lesson covered the conceptual side of testing: the test pyramid, the AAA shape, F.I.R.S.T. properties, and how to name a test so it reads like a sentence. This lesson is about the tool that actually runs those tests. JUnit 5 (also called Jupiter) is the de facto standard for Java testing, and almost every Java codebase has it set up already. This lesson wires it into a Maven and a Gradle project, writes a first test against an e-commerce class, and walks through the common parts of the API: assertions, lifecycle hooks, parameterized tests, nested grouping, exception testing, and mocking with Mockito.