如何在JUnit和Spring中测试void返回方法的java最佳实践？

Question

我不确定我是否以正确的方式测试了void返回方法，也不确定我的class-under-test（cut）是否需要任何更改以使其100%可测试和防bug

我在执行test时看到NullPointerException，因为loginOperations没有设置

错误：

java.lang.NullPointerException
    at com.demo.service.LoginService.doLogin(LoginService.java:40)
    at com.demo.service.LoginServiceTest.doLogin(LoginServiceTest.java:25)
    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.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$2.evaluate(ParentRunner.java:268)
    at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
    at org.junit.runner.JUnitCore.run(JUnitCore.java:137)
    at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:68)
    at com.intellij.rt.execution.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:47)
    at com.intellij.rt.execution.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:242)
    at com.intellij.rt.execution.junit.JUnitStarter.main(JUnitStarter.java:70)

登录服务。java

@Service
public class LoginService {

    @Autowired
    private ILoginOperations loginOperations;

    public void doLogin(HttpServletRequest request, String result) {
        LoginDTO loginDTO = new LoginDTO(request.getParameter("username"), result);
        loginOperations.doLogin(loginDTO);
    }
    
}

登录服务测试。java

public class LoginServiceTest {

    private LoginService instance = new LoginService();

    ILoginOperations loginOperations = Mockito.mock(ILoginOperations.class);
    HttpServletRequest request = Mockito.mock(HttpServletRequest.class);
    String result = "some string";

    @Test
    public void doLogin() {
        when(request.getParameter("username")).thenReturn("johndoe");
        instance.doLogin(request, result); //throws NPE while calling loginOperations.doLogin() because 
        assertNotNull(instance); //IS THIS THE CORRECT WAY TO TEST A VOID RETURNING METHOD ???
    }

}

现在，有两种方法可以修复测试

1. 我可以通过为loginOperations类添加setter方法并在test中调用setter方法来修复被测试的类
2. 将@Test public void doLogin() {更改为@Test(expected = Exception.class) public void doLogin() {

不确定上面哪一个是最佳实践以及原因

另一个问题：

我的另一个问题是如何对一个不返回任何内容的方法执行assert。有类似verify()的东西，但不确定如何使用它

Answer 1

一,。您可以通过在LoginService中添加setter方法来修复测试用例，也可以使用构造函数注入，比如-

@Autowired 
public LoginService(ILoginOperations loginOperations) {
    this.loginOperations = loginOperations;
}

1. 将异常验证为@Test(expected = Exception.class) public void doLogin()当然不是一个好主意，因为doLogin方法在正常情况下不会抛出异常

使用void返回类型测试方法的更好方法是使用验证API（示例-mockito verification API example）。您还可以使用Mockito的ArgumentCaptor捕获参数并断言该参数的状态，以及验证API，如下所示：

@RunWith(MockitoJUnitRunner.class)
public class LoginServiceTest {

    @Captor
    private ArgumentCaptor<LoginDTO> captor;
    @Mock
    private ILoginOperations loginOperations;
    @Mock
    private HttpServletRequest mockServletRequest;
    @InjectMocks
    private LoginService loginService;

    @Test
    public void validateLogin() {
        when(mockServletRequest.getParameter("username")).thenReturn("mock_user_name");
        loginService.doLogin(mockServletRequest, "mock_result");

        verify(loginOperations).doLogin(captor.capture());
        LoginDTO expectedLoginDTO = captor.getValue();
        
        assertThat(expectedLoginDTO.getResult(), is("mock_result"));
        assertThat(expectedLoginDTO.getUsername(), is("mock_user_name"));
    }
}

Martin Fowler有一篇关于这种测试方法的优秀文章——Mocks Aren't Stubs

Answer 2

实际上，你应该为你的LoginService创建一个构造函数来获取ILoginOperations，这样你就可以在测试类中创建LoginService，并将模拟的ILoginOperations作为参数传递，所有这些都应该在@Before方法中完成

或者你可以尝试使用@InjectMocks作为你的登录服务，并将你的ILoginOperations注释为@Mock