Mockito - MissingMethodInvocationException

Question

我正在尝试测试API调用是否在正确的调度程序上调度并在主线程上观察。

@RunWith(PowerMockRunner.class)
@PrepareForTest({Observable.class, AndroidSchedulers.class})
public class ProductsPresenterTest {
    private  ProductsPresenter presenter;
    @Before
    public void setUp() throws Exception{
        presenter = spy(new ProductsPresenter(mock(SoajsRxRestService.class)));
    }

    @Test
    public void testShouldScheduleApiCall(){
        Observable productsObservable = mock(Observable.class);
        CatalogSearchInput catalogSearchInput = mock(CatalogSearchInput.class);
        when(presenter.soajs.getProducts(catalogSearchInput)).thenReturn(productsObservable);
        /* error here*/ 
        when(productsObservable.subscribeOn(Schedulers.io())).thenReturn(productsObservable);
        when(productsObservable.observeOn(AndroidSchedulers.mainThread())).thenReturn(productsObservable);
        presenter.loadProducts(catalogSearchInput);
        //verify if all methods in the chain are called with correct arguments
        verify(presenter.soajs).getProducts(catalogSearchInput);
        verify(productsObservable).subscribeOn(Schedulers.io());
        verify(productsObservable).observeOn(AndroidSchedulers.mainThread());
        verify(productsObservable).subscribe(Matchers.<Subscriber<Result<Catalog<SoajsProductPreview>>>>any());
    }
}

该行

when(productsObservable.subscribeOn(Schedulers.io())).thenReturn(productsObservable);

抛出以下异常，我不明白为什么，因为 productObservable 是一个模拟。有什么想法或类似的经历吗？

org.mockito.exceptions.misusing.MissingMethodInvocationException: 
when() requires an argument which has to be 'a method call on a mock'.
For example:
    when(mock.getArticles()).thenReturn(articles);
Also, this error might show up because:
1. you stub either of: final/private/equals()/hashCode() methods.
   Those methods *cannot* be stubbed/verified.
   Mocking methods declared on non-public parent classes is not supported.
2. inside when() you don't call method on mock but on some other object.

Answer 1

问题是由于 Observable：：subscribeOn 是最终方法，Mockito 无法模拟。一种可能的解决方案是使用 Powermock：

@RunWith(PowerMockRunner.class)
@PrepareForTest(Observable.class)
public class MockTest {
    @Test
    public void test() {
        Observable productsObservable = PowerMockito.mock(Observable.class);
        when(productsObservable.subscribeOn(null)).thenReturn(productsObservable);
        productsObservable.subscribeOn(null);
        verify(productsObservable).subscribeOn(null);
    }
}