使用mockito在dropwizard中测试资源时出现NullPointerException

Question

我用dropwizard构建了一个restful API。现在我想用dropwizard文档提供的内容来测试它。

public class BlogCommentResourceTest {
private static final BlogCommentDAO dao = mock(BlogCommentDAO.class);
private final BlogComment blogComment = new BlogComment(1, "url", "comment", new Date(), "name");
@ClassRule
public static final ResourceTestRule resources = ResourceTestRule.builder()
.addResource(new BlogCommentResource(dao)).build();
List<BlogComment> list = new ArrayList<BlogComment>();
@Before
public void setUp(){
list.add(blogComment);
when(dao.getLast()).thenReturn(blogComment);
when(dao.getAll(POJOs.BlogCommentPOJO.toString())).thenReturn(list);
}
@After
public void tearDown(){
reset(dao);
}
@Test
public void getLast(){
assertThat(resources.client().target("/blogcomments").request().get(List.class))
.isEqualTo(list);
verify(dao.getAll(POJOs.BlogCommentPOJO.toString()), times(1));
}

}

这就是我想要测试的方法。

enter code here

错误信息如下所示：

java.lang.NullPointerException
at dao.DAOBase.getAll(DAOBase.java:37)
at dao.BlogCommentDAO.getAll(BlogCommentDAO.java:19)
at resource.BlogCommentResourceTest.setUp(BlogCommentResourceTest.java:29)
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.RunBefores.evaluate(RunBefores.java:24)
at org.junit.internal.runners.statements.RunAfters.evaluate(RunAfters.java:27)
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 io.dropwizard.testing.junit.ResourceTestRule$1.evaluate(ResourceTestRule.java:202)
at org.junit.rules.RunRules.evaluate(RunRules.java:20)
at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
at org.junit.runner.JUnitCore.run(JUnitCore.java:137)
at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:119)
at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:42)
at com.intellij.rt.execution.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:234)
at com.intellij.rt.execution.junit.JUnitStarter.main(JUnitStarter.java:74)
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 com.intellij.rt.execution.application.AppMain.main(AppMain.java:144)

有人知道发生了什么事吗？为什么是DAOBase抛出了一个空指针？我对所有dao的单元测试表明它们运行良好。

Answer 1

由于dao的mock为dao.DAOBase返回null，因此在dao.DAOBase.getAll(DAOBase.java:37)中引发异常。您似乎在嘲笑一个类，而不是一个接口，并试图访问这个被嘲笑类的字段。这是不起作用的，Mockito旨在模拟类支持有限的接口，并在其中模拟方法行为，而不是字段值。

要绕过你，最简单的方法是将你的BlogCommentDAO变成一个接口，或者如果它是一个类，那么至少上面有没有公共字段，这样就可以很容易地像一样被嘲笑

DAOBase daoBaseMock = mock(DAOBase.class)
doReturn(allThings).when(daoBaseMock).getAll();
doReturn(daoBaseMock).when(dao).DAOBase();