131-java-testing-unit-testing
Use when you need to review, improve, or write Java unit tests — including migrating from JUnit 4 to JUnit 5, adopting AssertJ for fluent assertions, structuring tests with Given-When-Then, ensuring test independence, applying parameterized tests, mocking dependencies with Mockito, verifying boundary conditions (RIGHT-BICEP, CORRECT, A-TRIP), leveraging JSpecify null-safety annotations, or eliminating testing anti-patterns such as reflection-based tests or shared mutable state. This should trigger for requests such as Review Java code for unit tests; Apply best practices for unit tests in Java code. Part of cursor-rules-java project
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- Repository
- jabrena/cursor-rules-java
- Last source activity
- June 15, 2026 at 16:07
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- English
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- 407
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- 81
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- 131-java-testing-unit-testing
- description
- Use when you need to review, improve, or write Java unit tests — including migrating from JUnit 4 to JUnit 5, adopting AssertJ for fluent assertions, structuring tests with Given-When-Then, ensuring test independence, applying parameterized tests, mocking dependencies with Mockito, verifying boundary conditions (RIGHT-BICEP, CORRECT, A-TRIP), leveraging JSpecify null-safety annotations, or eliminating testing anti-patterns such as reflection-based tests or shared mutable state. This should trigger for requests such as Review Java code for unit tests; Apply best practices for unit tests in Java code. Part of cursor-rules-java project
- license
- Apache-2.0
- metadata
- {"author":"Juan Antonio Breña Moral","version":"0.16.0"}
# Java Unit testing guidelines
Review and improve Java unit tests using modern JUnit 5, AssertJ, and Mockito best practices.
**What is covered in this Skill?**
- JUnit 5 annotations: `@Test`, `@BeforeEach`, `@AfterEach`, `@DisplayName`, `@Nested`, `@ParameterizedTest`
- AssertJ fluent assertions: `assertThat`, `assertThatThrownBy`
- Given-When-Then test structure, descriptive test naming, single-responsibility tests
- Test independence and isolated state
- Parameterized tests: `@ValueSource`/`@CsvSource`/`@MethodSource`
- Mockito dependency mocking: `@Mock`, `@InjectMocks`, `MockitoExtension`
- Code coverage guidance (JaCoCo), package-private test visibility
- Testing anti-patterns: reflection, shared state, hard-coded values, testing implementation details
- Error handling: `assertThatThrownBy`, exception messages
- JSpecify null-safety: `@NullMarked`, `@Nullable`
- RIGHT-BICEP coverage principles, A-TRIP test quality, CORRECT boundary condition verification
**Scope:** The reference is organized by examples (good/bad code patterns) for each core area. Apply recommendations based on applicable examples.
## Constraints
Before applying any unit test changes, ensure the project compiles. If compilation fails, stop immediately — do not proceed until resolved. After applying improvements, run full verification.
- **MANDATORY**: Run `./mvnw compile` or `mvn compile` before applying any change
- **SAFETY**: If compilation fails, stop immediately and do not proceed — compilation failure is a blocking condition
- **VERIFY**: Run `./mvnw clean verify` or `mvn clean verify` after applying improvements
- **BEFORE APPLYING**: Read the reference for detailed examples, good/bad patterns, and constraints
## When to use this skill
- Review Java code for unit tests
- Apply best practices for unit tests in Java code
## Workflow
1. **Compile project before unit-test changes**
Run `./mvnw compile` or `mvn compile` and stop immediately if compilation fails.
2. **Read unit-testing reference and evaluate coverage**
Read `references/131-java-testing-unit-testing.md` and identify modernization and quality gaps in current tests.
3. **Apply unit-testing best practices**
Implement or refactor tests using JUnit 5, AssertJ, Mockito, parameterization, and stronger boundary checks.
4. **Verify with full build**
Run `./mvnw clean verify` or `mvn clean verify` after applying improvements.
## Reference
For detailed guidance, examples, and constraints, see [references/131-java-testing-unit-testing.md](references/131-java-testing-unit-testing.md).
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