Mockito处于调试模式,断点导致返回值的类型错误

这里有一个简单的片段。

@Component
public class SomeDependency {
    public Optional<Integer> getSomeInt(String string) {
        return Optional.of(1);
    }
}

@Component
public class SomeService {

    @Autowired
    private SomeDependency someDependency;

    public String someMethod(String string) {
        return String.valueOf(someDependency.getSomeInt(string).get());
    }
}

@RunWith(MockitoJUnitRunner.class)
public class SomeServiceTest {

    @Mock
    private SomeDependency someDependency;

    @InjectMocks
    private SomeService someService;

    @Test
    public void test() {
        when(someDependency.getSomeInt(anyString()))
                .thenReturn(Optional.of(111));

        String value = someService.someMethod("test");

        assertThat(value, is("111"));
    }
}

现在,当我运行测试时,它运行正常,但是当我在调试模式下运行它时,断点处于打开状态时…然后返回。。。模拟和使用 step over ,引发以下错误。

org.mockito.exceptions.misusing.WrongTypeOfReturnValue:
        Optional cannot be returned by toString()
        toString() should return String
        ***
        If you're unsure why you're getting above error read on.
        Due to the nature of the syntax above problem might occur because:
        1. This exception *might* occur in wrongly written multi-threaded tests.
        Please refer to Mockito FAQ on limitations of concurrency testing.
        2. A spy is stubbed using when(spy.foo()).then() syntax. It is safer to stub spies -
        - with doReturn|Throw() family of methods. More in javadocs for Mockito.spy() method.

但是,如果我用一行而不是二行,那没关系。没有返回错误。

when(someDependency.getSomeInt(anyString())).thenReturn(Optional.of(111));

那么,问题在哪里?