Mockito：模拟 Hibernate Criteria uniqueResult 时出现 NullPointerException

Question

我正在学习 Mockito，我想要模拟 Hibernate 会话和方法 doubleCountAnimal(Session) 中使用的 Hibernate 标准：

public class ZooKeeper {

  public int doubleCountAnimal(Session session) {
    long rowCount = (long) session.createCriteria(Animal.class)
        .setProjection(Projections.rowCount())
        .uniqueResult();
    return (int) rowCount * 2;
  }
}

这是我用 Mockito 编写的单元测试：

public class ZooKeeperMockTest {

  private static final Animal[] animals = new Animal[] {new Animal("Cat"), new Animal("Dog")};
  private Session mockedSession;
  private Criteria mockedCriteria;

  @Before
  public void setUp() {
    mockedSession = Mockito.mock(Session.class);
    mockedCriteria = Mockito.mock(Criteria.class);

    Mockito.reset(mockedSession, mockedCriteria);
    // mock session
    Mockito.when(mockedSession.createCriteria(Animal.class)).thenReturn(mockedCriteria);
    // mock criteria
    Mockito.when(mockedCriteria.setProjection(Projections.rowCount())).thenReturn(mockedCriteria);
    Mockito.when(mockedCriteria.uniqueResult()).thenReturn((Object) (animals.length * 1L));
  }

  @Test
  public void testDoubleCountAnimal() {
    ZooKeeper zooKeeper = new ZooKeeper();
    assertEquals(animals.length * 2, zooKeeper.doubleCountAnimal(mockedSession));
  }
}

但是，当我运行测试时，我在下面的行中遇到异常：

        .uniqueResult();

我不明白为什么会出现此错误。我认为上述方法uniqueResult 的模拟在测试之前已经完成。有人可以帮忙吗？

Running io.mincongh.zoo.mockito.ZooKeeperMockTest
Tests run: 1, Failures: 0, Errors: 1, Skipped: 0, Time elapsed: 0.065 sec <<< FAILURE!
testDoubleCountAnimal(io.mincongh.zoo.mockito.ZooKeeperMockTest)  Time elapsed: 0.064 sec  <<< ERROR!
java.lang.NullPointerException
    at io.mincongh.zoo.ZooKeeper.doubleCountAnimal(ZooKeeper.java:14)
    at io.mincongh.zoo.mockito.ZooKeeperMockTest.testDoubleCountAnimal(ZooKeeperMockTest.java:42)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50)
    at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
    at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47)
    at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
    at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:26)
    at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325)
    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:78)
    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:57)
    at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290)
    at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71)
    at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)
    at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58)
    at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268)
    at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
    at org.apache.maven.surefire.junit4.JUnit4Provider.execute(JUnit4Provider.java:252)
    at org.apache.maven.surefire.junit4.JUnit4Provider.executeTestSet(JUnit4Provider.java:141)
    at org.apache.maven.surefire.junit4.JUnit4Provider.invoke(JUnit4Provider.java:112)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at org.apache.maven.surefire.util.ReflectionUtils.invokeMethodWithArray(ReflectionUtils.java:189)
    at org.apache.maven.surefire.booter.ProviderFactory$ProviderProxy.invoke(ProviderFactory.java:165)
    at org.apache.maven.surefire.booter.ProviderFactory.invokeProvider(ProviderFactory.java:85)
    at org.apache.maven.surefire.booter.ForkedBooter.runSuitesInProcess(ForkedBooter.java:115)
    at org.apache.maven.surefire.booter.ForkedBooter.main(ForkedBooter.java:75)


Results :

Tests in error: 
  testDoubleCountAnimal(io.mincongh.zoo.mockito.ZooKeeperMockTest)

我的问题与模拟框架有关，请不要将其作为简单NullPointerException的副本关闭。

Answer 1

感谢Jim Garrison在评论中的帮助，我发现了错误。

错误似乎是模拟的Criteria#setProjection() 返回null 而不是这个以允许方法链接。我已经很多年没有使用 Mockito 了，但是否有某种方法可以覆盖嘲笑以返回 this？

答案是肯定的，有一种方法可以在单元测试中使用Mockito#anyObject：

Mockito.when(mockedCriteria.setProjection((Projection) Mockito.anyObject()))
    .thenReturn(mockedCriteria);