JUnit 测试用例：java.lang.NullPointerException答案

【问题标题】：JUnit test case: java.lang.NullPointerExceptionJUnit 测试用例：java.lang.NullPointerException
【发布时间】：2018-04-25 10:14:53
【问题描述】：

我正在尝试使用JUnit 和mockito 为以下控制器代码编写测试用例。但我得到空指针异常。我是 JUnit 测试的新手。谁能告诉我在这里做错了什么？

部门控制器

   @RestController
    @RequestMapping("/api.spacestudy.com/SpaceStudy")
    public class DepartmentController {

        @Autowired
        DepartmentService depService;

        @CrossOrigin(origins = "http://localhost:4200")
        @GetMapping("/LoadDept")
        public  Department findDeptId() {
            return  depService.findDeptId();
        }
    }

DepaermentControllerTest

 @WebMvcTest
    public class DepartmentControllerTest {

        @Autowired
        private MockMvc mockMvc;

       @Mock
       public DepartmentService depService;  

       @InjectMocks
       DepartmentController departmentController;

       @Before
        public void setup() throws Exception    {
            mockMvc = MockMvcBuilders.standaloneSetup(departmentController).build(); 
        }


       @Test
       public void findDeptIdTest() throws Exception
       {

           Department department = new Department();
           department.setnDeptId(10);

           Mockito.when(depService.findDeptId()).thenReturn(department);

        mockMvc.perform(get("/api.spacestudy.com/SpaceStudy/LoadDept").accept(MediaType.APPLICATION_JSON))
                .andExpect(status().isOk())
                .andExpect(jsonPath("$.nDeptId", Matchers.is(10)));         
       }

    }

测试结果

java.lang.NullPointerException
    at org.springframework.web.servlet.handler.AbstractHandlerMethodMapping.detectHandlerMethods(AbstractHandlerMethodMapping.java:227)
    at org.springframework.test.web.servlet.setup.StandaloneMockMvcBuilder$StaticRequestMappingHandlerMapping.registerHandlers(StandaloneMockMvcBuilder.java:490)
    at org.springframework.test.web.servlet.setup.StandaloneMockMvcBuilder.registerMvcSingletons(StandaloneMockMvcBuilder.java:356)
    at org.springframework.test.web.servlet.setup.StandaloneMockMvcBuilder.initWebAppContext(StandaloneMockMvcBuilder.java:341)
    at org.springframework.test.web.servlet.setup.AbstractMockMvcBuilder.build(AbstractMockMvcBuilder.java:139)
    at com.spacestudy.DepartmentControllerTest.setup(DepartmentControllerTest.java:38)
    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.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.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:86)
    at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:538)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:760)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:460)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:206)

【问题讨论】：

你谷歌春季测试教程了吗？
是的，我阅读了教程并尝试了上面的代码
我的测试正在运行。我将@WebMvcTest 更改为@RunWith(SpringJUnit4ClassRunner.class)
将此作为答案发布并关闭。
好的，我会发帖的。但是我能告诉我为什么会因为那个注释而出现这个问题

标签： unit-testing spring-data-jpa mockito junit4

【解决方案1】：

要解决这个问题，你必须在standaloneSetup() 中提供一个DepartmentController 类的实例。我在进行一些单元测试时遇到了同样的问题，之后我的问题就消失了。试着去做：

@Before
public void setup() throws Exception    {
      mockMvc = MockMvcBuilders.standaloneSetup(new DepartmentController()).build(); 
}

【讨论】：