Mocking Spring @Value in Unit Tests

Mocking @Value in Spring Boot Unit Tests

Spring's @Value annotation injects values from properties files. For unit tests, mocking this is crucial for isolation. Avoid testing external dependencies.

Method 1: Using @SpringBootTest and @TestPropertySource (Integration Test)

This approach is useful when you need to test the interaction with properties, but it's not a pure unit test.

@SpringBootTest
@TestPropertySource(properties = {"my.property=testValue"})
class MyServiceTest {
    @Value("${my.property}")
    String myProperty;

    @Test
    void testMyMethod() {
        assertEquals("testValue", myProperty);
    }
}

Method 2: Using MockBean (Unit Test)

This is preferred for pure unit tests. You directly mock the dependency. Requires a constructor injection or setter for myProperty.

@ExtendWith(MockitoExtension.class)
class MyServiceTest {
    private final String myProperty;
    private MyService myService;

    @InjectMocks
    MyService myService;

    @Mock
    private String myProperty;

    @BeforeEach
    public void setUp(){
        MockitoAnnotations.openMocks(this);
    }

    @Test
    void testMyMethod() {
        Mockito.when(myProperty).thenReturn("testValue");
        //Use myService
    }
}

Method 3: Constructor Injection and Direct Instantiation (Unit Test)

This gives you the most control, bypassing Spring entirely. Suitable for simple cases.

class MyService {
    private final String myProperty;
    MyService(String myProperty){
        this.myProperty = myProperty;
    }
    // ... your methods
}
@Test
void testMyMethod(){
    MyService service = new MyService("testValue");
    // ... test using service
}

Choose the method that best suits your testing needs. Prioritize unit tests (Methods 2 & 3) for faster, isolated testing. Use integration tests (Method 1) sparingly for broader system verification. Remember to add necessary dependencies like Mockito and spring-test.