Different mocks are used for @Mock and @InjectMock in the same test class with JUnit 5 extension when using SpringExtension.class along with MockitoExtension.class

[karthikairam]

I'm seeing this same bug when using SpringExtension.class along with MockitoExtension.class:

@ExtendWith({MockitoExtension.class, SpringExtension.class})
public class InjectMocksTest {
  static class TacticalStation {}

  static class SpaceShip {
    private final TacticalStation tacticalStation;

    public SpaceShip(final TacticalStation tacticalStation) {
      this.tacticalStation = tacticalStation;
    }

    public TacticalStation getTacticalStation() {
      return tacticalStation;
    }
  }

  @InjectMocks
  private SpaceShip spaceShip;

  @Mock
  private TacticalStation tacticalStation;

  @Test
  public void shouldInjectMocks() {
    assertThat(tacticalStation).isNotNull();
    assertThat(spaceShip.getTacticalStation()).isEqualTo(tacticalStation);
    //Bug ↑ - different mocks are use in @Mock and @InjectMock
  }
}

This is using Mockito 3.1.0, JUnit 5.6.0, and Spring Boot 5.3.0.RELEASE.

Yes I am also facing this issue. Mine is also exactly the same scenario. Below are my dependencies,
org.junit.jupiter:junit-jupiter-engine:5.6.0
org.springframework.boot:spring-boot-starter:2.2.6.RELEASE
org.springframework.boot:spring-boot-starter-test:2.2.6.RELEASE
org.mockito:mockito-junit-jupiter:3.1.0

Originally posted by @karthikaiselvan in #1346 (comment)

[andreisilviudragnea]

The reason why the test fails is that both MockitoTestExecutionListener from spring-boot-test and the MockitoExtension call MockitoAnnotations.init() on the test class instance.

Only the first init() call sets the value of the field spaceShip, with an object that refers the @Mock-annotated field tacticalStation injected by the first init() call.

The second init() call does not set another value for the spaceShip field, because this is how @InjectMocks works. If the field already has a value, it does not change it anymore. I found this behavior surprising myself and I believe this is a good reason why @InjectMocks should be avoided (#1518). However, the second init() call injects a new mock into the tacticalStation and thus the test fails.

As a side note, what are you trying to achieve by using both MockitoExtension and SpringExtension?

If you write a Mockito-strict unit test, just use MockitoExtension and you are done.

If you write a Mockito-strict Spring integration test, MockitoExtension is useless, because Spring integration tests do not have support for strict stubbing yet. It is a bit harder to implement, given the complexity added by Spring Application Context caching. I am working on a proposal in both Mockito and Spring Boot test for this to be implemented. For now, in the case of Spring integration tests, just use the @MockBean annotation from Spring Boot test to do your job.