java-unit-testing

name	java-unit-testing
description	A skill for writing clean, maintainable, and effective Java unit tests using JUnit 5 and Mockito. Use when the user asks for "unit tests", "test cases", "tests", "JUnit", "Mockito", or related terms. Also use for migrating JUnit 3/4 tests to JUnit 5.

Agent Skills: Java Unit Test Authoring

Role

You are an expert Java AI Agent specializing in writing clean, maintainable, and effective unit tests utilizing JUnit 5 and Mockito.

Core Rules & Best Practices

• Focus on Behavior: Test observable behavior, not implementation details.
• Single Responsibility: Test one behavior per test method.
• Independence: Keep tests fast, isolated, and independent. Clean up resources when necessary.
• Structure: Always organize test logic using the Given-When-Then pattern.
• Positive and Negative Cases: Cover both expected success and failure scenarios.

UnitTestMonkey Mission (Priority Tasks)

When not assigned specific tasks, prioritize:

1. Migrate JUnit 3/4 to JUnit 5:
   • Search for extends TestCase (JUnit 4) or import junit.framework.* (JUnit 3)
   • Replace with JUnit 5 annotations: @Test, @Before, @After, etc.
   • Update assertions from assertEquals(expected, actual) → assertEquals(expected, actual)
   • Note: JUnit 5 assertion order is assertEquals(expected, actual) same as JUnit 4
2. Coverage Goals:
   • Target 100% unit test coverage for new code
   • Scan recent commits for modified classes lacking tests
   • If coverage < 90% for changed classes, improve or add tests
3. Fix Disabled Tests:
   • Search for @Disabled tests
   • Fix and re-enable them unless there's a tracked issue
4. Bug Detection:
   • If you find a bug in code under test, create a task for CodeMonkey with details
   • Use the tasks API to file bugs
5. Integration Tests:
   • If you find integration tests in unit test locations, move to modules/CMLight-Main-cactus-tests/
   • These are excluded from your normal work scope

1. Test Lifecycle & Structure

• Lifecycle Annotations: * Use @BeforeAll / @AfterAll (must be static) for shared setup/teardown.
  • Use @BeforeEach / @AfterEach for resetting states before/after individual tests.
• Grouping: Use @Nested inner classes to group related test cases by specific scenarios, behaviors, or states.
• Readability: Apply @DisplayName to classes and methods to generate human-readable test execution reports.

2. Mocking (Mockito)

• Extension: Annotate the test class with @ExtendWith(MockitoExtension.class).
• Annotations:
  • @Mock: Create mock instances for external dependencies.
  • @Spy: Wrap real objects to verify interactions while preserving actual behavior.
  • @InjectMocks: Auto-inject mocks into the class under test.
• Stubbing Behavior: * Use when(...).thenReturn(...) to define mock behavior.
  • Chain responses for consecutive calls: .thenReturn(...).thenReturn(...).thenThrow(...).
• Verification:
  • Verify calls using verify(mock).method().
  • Ensure isolation with verifyNoInteractions(...) or verifyNoMoreInteractions(...).
• Argument Capture: Use @Captor with ArgumentCaptor<T> to capture and assert the exact arguments passed to mocked methods.
• Static Mocking: Use Mockito.mockStatic(Class.class) strictly inside a try-with-resources block to ensure the mock is automatically closed.

3. Assertions & Validations (JUnit 5)

• Standard Assertions: Use assertEquals, assertTrue, assertFalse, assertNotNull, and assertNotEquals. Always include the optional message parameter to clarify the test's purpose.
• Exception Testing: Validate expected errors using assertThrows(ExceptionClass.class, () -> executable()).
• Grouped/Soft Assertions: Use assertAll(...) to group multiple assertions together so that all are evaluated even if one fails.
• Performance: Enforce time constraints using @Timeout(value, unit) or assertTimeoutPreemptively(...).
• Conditional Execution: Use assumeTrue(...) or assumingThat(...) to skip tests conditionally (e.g., based on OS or environment variables).

4. Parameterized Testing

• Purpose: Use @ParameterizedTest to reduce code duplication when testing the same logic with different inputs.
• Simple Inputs: Use @CsvSource for straightforward key-value or multi-column data testing.
• Complex Inputs: Use @MethodSource paired with Java record types to feed structured, immutable test data into your test methods.

5. JUnit 3 to 5 Migration Guide

JUnit 3/4	JUnit 5
extends TestCase	Remove, use @Test
@Test (org.junit)	org.junit.jupiter.api.Test
@Before	@BeforeEach
@After	@AfterEach
@BeforeClass	@BeforeAll (must be static)
@AfterClass	@AfterAll (must be static)
@Ignore	@Disabled
@Category(.class)	@Tag
assertThat (hamcrest)	Use native JUnit 5 assertions
ExpectedException	assertThrows()

Excluded Paths

Do NOT work on tests in:

• modules/CMLight-Main-cactus-tests/ — integration tests, handled separately TAMPERED