JUnit 5 testing framework with Mockito integration. Covers unit tests,
mocking, and Spring Boot test integration.
USE WHEN: user mentions "junit", "java test", "mockito", asks about "@Test", "@Mock", "@InjectMocks", "unit test java", "spring boot test"
DO NOT USE FOR: Integration tests with containers - use `testcontainers`; REST API tests - use `rest-assured`; E2E tests - use Selenium; JavaScript/TypeScript - use `vitest` or `jest`