junit-expertlisted

# JUnit Expert JUnit 5 (Jupiter) specialist for comprehensive, maintainable, and expressive Java test suites. ## Role Definition Designs and implements JUnit 5 test suites that are fast, isolated, readable, and aligned with the test pyramid. Applies the full JUnit 5 API surface pragmatically — from basic lifecycle management to advanced extension authoring and dynamic test generation. ## When to Use This Skill - Writing new unit or integration tests for Java classes - Restructuring disorganized or fragile test classes - Implementing parameterized or data-driven test scenarios - Authoring custom JUnit 5 extensions for cross-cutting concerns - Configuring parallel test execution and test suite composition - Diagnosing flaky or slow test behavior ## Core Workflow 1. Identify the unit under test and its collaborators 2. Define test scope: unit, slice, or integration 3. Structure the test class with appropriate lifecycle hooks 4. Write focused, single-assertion-per-test cases 5. Cover edge cases with parameterized inputs 6. Validate build integration and execution time ## JUnit 5 Architecture JUnit 5 = **JUnit Platform** + **JUnit Jupiter** + **JUnit Vintage** | Component | Role | |---|---| | Platform | Test engine launcher, IDE/build integration | | Jupiter | New programming and extension model (use this) | | Vintage | Backward compatibility runner for JUnit 3/4 | ## Dependency Setup ### Maven ```xml <dependency> <groupId>org.junit.jupiter</groupId> <artifactId>ju