单元测试，我无法将Observer添加到LiveData NullPointerException

Question

为什么即使我删除观察者并使用mLivedata.getValue（）和assertNotNull（mLiveData），它仍能正常工作吗？

@RunWith(PowerMockRunner.class)
public class LoginRepositoryTest {

   //Data
   LoginRepository loginRepository;


   @Rule
   InstantTaskExecutorRule rule = new InstantTaskExecutorRule();


   @Mock
   AppExecutors appExecutors;
   @Mock
   LoginService loginService;
   @Mock
   Observer<Resource<Session>> loginObserver;
   @Mock
   ApiResponse<Session> loginResponse;
   @Mock
   ArgumentCaptor<Resource<Session>> resultLDCaptor;
   @Before
   public void setUp(){
       MockitoAnnotations.initMocks(this);
       RxAndroidPlugins.setInitMainThreadSchedulerHandler(scheduler -> Schedulers.trampoline());
       loginRepository=spy(new LoginRepository(appExecutors,loginService));
   }

   @Test
   public void testLoginSuccess(){


       //Prepare Login service
       MutableLiveData<ApiResponse<Session>> serviceLD=spy(new MutableLiveData<>());
       when(loginService.login(mock(RequestBody.class))).thenReturn(serviceLD);

       //Perform Login
       loginRepository.login(mock(RequestBody.class)).observeForever(loginObserver);

       //capture any value
       verify(loginObserver).onChanged(resultLDCaptor.capture());

       //Now value must be Resource.Loading
       assertNotNull(resultLDCaptor.getValue());
       assertTrue(resultLDCaptor.getValue().isLoading());

       //Now return fake data from server
       when(loginResponse.isSuccessful()).thenReturn(true);
       loginResponse.data=mock(Session.class);
       serviceLD.postValue(loginResponse);

   }

和错误

java.lang.NullPointerException在android.arch.lifecycle.MediatorLiveData $ Source.plug（MediatorLiveData.java:141）在android.arch.lifecycle.MediatorLiveData.onActive（MediatorLiveData.java:118）在android.arch.lifecycle.LiveData $ ObserverWrapper.activeStateChanged（LiveData.java:410）在android.arch.lifecycle.LiveData.observeForever（LiveData.java:207）在com.wimoapp.android.login.LoginRepositoryTest.testLoginSuccess（LoginRepositoryTest.java:74）在sun.reflect.NativeMethodAccessorImpl.invoke0（本机方法）处在sun.reflect.NativeMethodAccessorImpl.invoke（NativeMethodAccessorImpl.java:62）在sun.reflect.DelegatingMethodAccessorImpl.invoke（DelegatingMethodAccessorImpl.java:43）在java.lang.reflect.Method.invoke（Method.java:498）在org.junit.internal.runners.TestMethod.invoke（TestMethod.java:68）在org.powermock.modules.junit4.internal.impl.PowerMockJUnit44RunnerDelegateImpl $ PowerMockJUnit44MethodRunner.runTestMethod（PowerMockJUnit44RunnerDelegateImpl.java:310）处在org.junit.internal.runners.MethodRoadie $ 2.run（MethodRoadie.java:89）在org.junit.internal.runners.MethodRoadie.runBeforesThenTestThenAfters（MethodRoadie.java:97）在org.powermock.modules.junit4.internal.impl.PowerMockJUnit44RunnerDelegateImpl $ PowerMockJUnit44MethodRunner.executeTest（PowerMockJUnit44RunnerDelegateImpl.java:294）在org.powermock.modules.junit4.internal.impl.PowerMockJUnit47RunnerDelegateImpl $ PowerMockJUnit47MethodRunner.executeTestInSuper（PowerMockJUnit47RunnerDelegateImpl.java:131）上at org.powermock.modules.junit4.internal.impl.PowerMockJUnit47RunnerDelegateImpl $ PowerMockJUnit47MethodRunner.access $ 100（PowerMockJUnit47RunnerDelegateImpl.java:59）在org.powermock.modules.junit4.internal.impl.PowerMockJUnit47RunnerDelegateImpl $ PowerMockJUnit47MethodRunner $ TestExecutorStatement.evaluate（PowerMockJUnit47RunnerDelegateImpl.java:147）中在org.junit.rules.TestWatcher $ 1.evaluate（TestWatcher.java:55）在org.powermock.modules.junit4.internal.impl.PowerMockJUnit47RunnerDelegateImpl $ PowerMockJUnit47MethodRunner.evaluateStatement（PowerMockJUnit47RunnerDelegateImpl.java:107）上在org.powermock.modules.junit4.internal.impl.PowerMockJUnit47RunnerDelegateImpl $ PowerMockJUnit47MethodRunner.executeTest（PowerMockJUnit47RunnerDelegateImpl.java:82）处在org.powermock.modules.junit4.internal.impl.PowerMockJUnit44RunnerDelegateImpl $ PowerMockJUnit44MethodRunner.runBeforesThenTestThenAfters（PowerMockJUnit44RunnerDelegateImpl.java:282）上在org.junit.internal.runners.MethodRoadie.runTest（MethodRoadie.java:87）在org.junit.internal.runners.MethodRoadie.run（MethodRoadie.java:50）在org.powermock.modules.junit4.internal.impl.PowerMockJUnit44RunnerDelegateImpl.invokeTestMethod（PowerMockJUnit44RunnerDelegateImpl.java:202）处在org.powermock.modules.junit4.internal.impl.PowerMockJUnit44RunnerDelegateImpl.runMethods（PowerMockJUnit44RunnerDelegateImpl.java:144）在org.powermock.modules.junit4.internal.impl.PowerMockJUnit44RunnerDelegateImpl $ 1.run（PowerMockJUnit44RunnerDelegateImpl.java:118）在org.junit.internal.runners.ClassRoadie.runUnprotected（ClassRoadie.java:34）在org.junit.internal.runners.ClassRoadie.runProtected（ClassRoadie.java:44）在org.powermock.modules.junit4.internal.impl.PowerMockJUnit44RunnerDelegateImpl.run（PowerMockJUnit44RunnerDelegateImpl.java:120）在org.powermock.modules.junit4.common.internal.impl.JUnit4TestSuiteChunkerImpl.run（JUnit4TestSuiteChunkerImpl.java:121）在org.powermock.modules.junit4.common.internal.impl.AbstractCommonPowerMockRunner.run（AbstractCommonPowerMockRunner.java:53）在org.powermock.modules.junit4.PowerMockRunner.run（PowerMockRunner.java:59）在org.junit.runner.JUnitCore.run（JUnitCore.java:137）在com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs（JUnit4IdeaTestRunner.java:68）在com.intellij.rt.execution.junit.IdeaTestRunner $ Repeater.startRunnerWithArgs（IdeaTestRunner.java:47）在com.intellij.rt.execution.junit.JUnitStarter.prepareStreamsAndStart（JUnitStarter.java:242）在com.intellij.rt.execution.junit.JUnitStarter.main（JUnitStarter.java:70）

Answer 1

确保MediatorLiveData观察到的任何实时数据都不为空：

myMediatorLiveData.addSource(repository.getLiveData(), ...);
                                        ^^^^^^^^^^^

在我的情况下，因为repository.getLiveData()被嘲笑，所以repository返回null。在测试中，您可以使用Mockito轻松返回实时数据实例，例如：

MutableLiveData<...> liveData = new MutableLiveData<>();    
when(repository.getLiveData()).thenReturn(liveData);