如果我是您，我会简单地模拟服务A和B以及执行器，然后通过注解@InjectMocks注入它们，因为它们是类的字段。
如果你想模拟Executor的方法execute，你应该按照下面的步骤简单地调用所提供的Runnable的方法run：

doAnswer(
    (InvocationOnMock invocation) -> {
        ((Runnable) invocation.getArguments()[0]).run();
        return null;
    }
).when(serviceAExecutorService).execute(any(Runnable.class));

所以基本上你的测试应该是这样的：

@RunWith(MockitoJUnitRunner.class)
public class CompletableFutureServiceTest {

    // The mock of my service A
    @Mock
    private ServiceA ServiceA;
    // The mock of my service B
    @Mock
    private ServiceB ServiceB;
    // The mock of your executor for the service A
    @Mock
    private Executor serviceAExecutorService;
    // The mock of your executor for the service B
    @Mock
    private Executor serviceBExecutorService;
    // My class in which I want to inject the mocks
    @InjectMocks
    private CompletableFutureService service;

    @Test
    public void testSomeMethod() {
        // Mock the method execute to call the run method of the provided Runnable
        doAnswer(
            (InvocationOnMock invocation) -> {
                ((Runnable) invocation.getArguments()[0]).run();
                return null;
            }
        ).when(serviceAExecutorService).execute(any(Runnable.class));
        doAnswer(
            (InvocationOnMock invocation) -> {
                ((Runnable) invocation.getArguments()[0]).run();
                return null;
            }
        ).when(serviceBExecutorService).execute(any(Runnable.class));

        ServiceAResponse serviceAResponse = ... // The answer to return by service A
        // Make the mock of my service A return my answer
        when(ServiceA.retrieve(any(ServiceARequest.class))).thenReturn(
            serviceAResponse
        );
        ServiceBResponse serviceBResponse = ... // The answer to return by service B
        // Make the mock of my service B return my answer
        when(ServiceB.retrieve(any(ServiceBRequest.class))).thenReturn(
            serviceBResponse
        );

        // Execute my method
        ServiceResponse response = service.someMethod(
            new ServiceARequest(), new ServiceBRequest()
        );

        // Test the result assuming that both responses are wrapped into a POJO
        Assert.assertEquals(serviceAResponse, response.getServiceAResponse());
        Assert.assertEquals(serviceBResponse, response.getServiceBResponse());
    }
}

@Mock
  private AsyncExecuter asyncExecuter;
  @Mock
  private CompletableFuture<XyzSample> xyzSampleResponse;
  @Mock
  private CompletableFuture<Map<String, String>> abcSampleResponse;

 @Before
  public void setUp() throws Exception {

    abcSampleResponse = CompletableFuture.completedFuture(TestUtil.readJsonResource(
        "misc_mapper_response.json", new TypeReference<Map<String, String>>() {
        }));

    xyzSampleResponse = CompletableFuture.completedFuture(TestUtil.readJsonResource(
        "gp_facade_response.json", new TypeReference<XyzSample>() {
        }));

  }

   @Test
  public void testAbcMethod() {

    Mockito.doReturn(abcSampleResponse).when(asyncExecuter)
        .callPgEndpoint(TestConstants.TEST_CUSTOMER_ID);

    Mockito.doReturn(xyzSampleResponse).when(asyncExecuter)
        .getUserPreference(TestConstants.TEST_CUSTOMER_ID);

    final ActualResponse actualResponse = globalPositionService
        .getGlobalPosition(TestConstants.TEST_CUSTOMER_ID);

    assertNotNull(actualResponse);
}

=====Service
public ActualResponse getGlobalPosition(final String customerId) {

    final CompletableFuture<Map<String, String>> abcSampleResponse = asyncExecuter
        .getProductTypeInfo();
    final CompletableFuture<XyzSample> xyzSampleResponse = asyncExecuter
        .getUserPreference(customerId);

    try {
      return new ResponseDecorator(pgResponse.get(), userPreferenceResponse.get(),
          productTypeInfo.get()).decorate();
    } catch (final Exception e) {
      log.error("Error Occurred while building the response", e);
    }
    return null;
  }

@Component
public class AsyncExecuter {
  public CompletableFuture<XyzSample> callPgEndpoint(final String customerId) {
    return CompletableFuture.completedFuture(xxx);
  }
}

我已经为JUnit5和Mockito解决了这个问题

@Spy ThreadPoolTaskExecutor spyTaskExecutor = new ThreadPoolTaskExecutor();

还有

@BeforeEach
void setUp() {
    openMocks(this);
    spyTaskExecutor.setCorePoolSize(1);
    spyTaskExecutor.setWaitForTasksToCompleteOnShutdown(true);
    spyTaskExecutor.initialize();
}