java-junit

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JUnit 5 best practices for standard and data-driven unit testing with practical patterns. Covers test structure using Arrange-Act-Assert pattern, lifecycle annotations ( @BeforeEach , @AfterEach , @BeforeAll , @AfterAll ), and naming conventions with @DisplayName Parameterized testing via @ParameterizedTest with multiple sources: @ValueSource , @MethodSource , @CsvSource , @CsvFileSource , and @EnumSource Assertion strategies including static Assertions methods, AssertJ fluent syntax,... npx skills add https://github.com/github/awesome-copilot --skill java-junit Download ZIPGitHub36.2k

JUnit 5+ Best Practices

Your goal is to help me write effective unit tests with JUnit 5, covering both standard and data-driven testing approaches.

Test Structure

• Test classes should have a Test suffix, e.g., CalculatorTest for a Calculator class.

• Use @Test for test methods.

• Follow the Arrange-Act-Assert (AAA) pattern.

• Name tests using a descriptive convention, like methodName_should_expectedBehavior_when_scenario.

• Use @BeforeEach and @AfterEach for per-test setup and teardown.

• Use @BeforeAll and @AfterAll for per-class setup and teardown (must be static methods).

• Use @DisplayName to provide a human-readable name for test classes and methods.

Standard Tests

• Keep tests focused on a single behavior.

• Avoid testing multiple conditions in one test method.

• Make tests independent and idempotent (can run in any order).

• Avoid test interdependencies.

Data-Driven (Parameterized) Tests

• Use @ParameterizedTest to mark a method as a parameterized test.

• Use @ValueSource for simple literal values (strings, ints, etc.).

• Use @MethodSource to refer to a factory method that provides test arguments as a Stream, Collection, etc.

• Use @CsvSource for inline comma-separated values.

• Use @CsvFileSource to use a CSV file from the classpath.

• Use @EnumSource to use enum constants.

Assertions

• Use the static methods from org.junit.jupiter.api.Assertions (e.g., assertEquals, assertTrue, assertNotNull).

• For more fluent and readable assertions, consider using a library like AssertJ (assertThat(...).is...).

• Use assertThrows or assertDoesNotThrow to test for exceptions.

• Group related assertions with assertAll to ensure all assertions are checked before the test fails.

• Use descriptive messages in assertions to provide clarity on failure.

Mocking and Isolation

• Use a mocking framework like Mockito to create mock objects for dependencies.

• Use @Mock and @InjectMocks annotations from Mockito to simplify mock creation and injection.

• Use interfaces to facilitate mocking.

Test Organization

• Group tests by feature or component using packages.

• Use @Tag to categorize tests (e.g., @Tag("fast"), @Tag("integration")).

• Use @TestMethodOrder(MethodOrderer.OrderAnnotation.class) and @Order to control test execution order when strictly necessary.

• Use @Disabled to temporarily skip a test method or class, providing a reason.

• Use @Nested to group tests in a nested inner class for better organization and structure.