spring-tdd-mockito

Testing & Quality

TDD (Test-Driven Development) skill with Mockito for Spring Boot. Guides the Red-Green-Refactor cycle for writing tests first.

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Spring Boot TDD with Mockito

TDD Cycle: Red → Green → Refactor

┌─────────────────────────────────────────────────────────────┐
│                     TDD WORKFLOW                             │
│                                                              │
│   ┌───────┐      ┌───────┐      ┌──────────┐               │
│   │  RED  │ ───→ │ GREEN │ ───→ │ REFACTOR │ ───┐          │
│   │       │      │       │      │          │    │          │
│   │ Write │      │ Write │      │ Improve  │    │          │
│   │ Test  │      │ Code  │      │ Code     │    │          │
│   └───────┘      └───────┘      └──────────┘    │          │
│       ↑                                          │          │
│       └──────────────────────────────────────────┘          │
└─────────────────────────────────────────────────────────────┘

Mockito Annotations

Annotation	Purpose
`@Mock`	Create mock object
`@InjectMocks`	Inject mocks into class under test
`@Spy`	Partial mock - real methods + mock behavior
`@Captor`	Capture arguments passed to mock
`@MockBean`	Mock bean in Spring context

Test Template

@ExtendWith(MockitoExtension.class)
class ServiceTest {

    @Mock
    private Repository repository;

    @InjectMocks
    private Service service;

    @Test
    @DisplayName("Should do something when condition is met")
    void shouldDoSomethingWhenConditionIsMet() {
        // Given (Arrange)
        when(repository.findById(1L)).thenReturn(Optional.of(entity));

        // When (Act)
        var result = service.doSomething(1L);

        // Then (Assert)
        assertThat(result).isNotNull();
        verify(repository).findById(1L);
    }
}

Best Practices

One assertion per test - Focus on single behavior
Descriptive test names - Use @DisplayName
AAA Pattern - Arrange, Act, Assert
Test behavior, not implementation
Fast tests - Mock external dependencies
Isolated tests - No shared state