testing-java

name	testing-java
description	Java testing with JUnit 5 and Mockito: test lifecycle, mocking, and integration test patterns

Testing — Java

Framework

• JUnit 5 (@Test, @BeforeEach, @AfterEach, @ParameterizedTest).
• Mockito for mocking.
• Run: mvn test / gradle test

Test Structure

@ExtendWith(MockitoExtension.class)
class OrderServiceTest {

    @Mock
    private PaymentGateway paymentGateway;

    @InjectMocks
    private OrderService orderService;

    @Test
    void shouldThrowOrderExceptionWhenPaymentFails() {
        // Arrange
        when(paymentGateway.charge(any())).thenThrow(new PaymentException("Declined"));

        // Act & Assert
        assertThrows(OrderException.class, () -> orderService.placeOrder(testOrder()));
    }
}

Parameterized Tests

@ParameterizedTest
@ValueSource(strings = {"", " ", "\t"})
void shouldReturnTrueForBlankStrings(String value) {
    assertTrue(StringUtils.isBlank(value));
}

Mocking Rules

• Use @Mock and @InjectMocks with MockitoExtension — avoid Mockito.mock() in tests.
• Verify critical interactions: verify(paymentGateway, times(1)).charge(expectedAmount).
• Use @Captor to capture and assert arguments passed to mocks.

Integration Tests

• Annotate with @SpringBootTest for full context; @WebMvcTest for controller slice only.
• Use an in-memory DB (H2) for repository tests.
• Separate integration tests into src/integrationTest/ and run in a separate Gradle task.

Coverage

• Target 80%+ line coverage on service/domain layers.
• Use JaCoCo: gradle jacocoTestReport and enforce with jacocoTestCoverageVerification.