Mockito 如何 mock 静态方法

在实际工作当中，我们经常会遇到需要对静态方法进行 mock 的情况。在 mockito 2.x 的时代，我们需要借助 powmock 才能实现。当 mockito 进化到了 3.4.0 版本以后，也开始对静态方法 mock 进行了支持（主要是通过 mockito-inline 包）。

简单的介绍就到这里，下面让我们进入主题吧。

1. 首先确保 pom 文件中 mockito 相关 jar 包的版本（这里我用的版本是 3.7.7），如下：

   <dependency>
       <groupId>org.mockitogroupId>
       <artifactId>mockito-coreartifactId>
       <version>3.7.7version>
       <scope>testscope>
   dependency>
   <dependency>
       <groupId>org.mockitogroupId>
       <artifactId>mockito-inlineartifactId>
       <version>3.7.7version>
       <scope>testscope>
   dependency>
   <dependency>
       <groupId>org.mockitogroupId>
       <artifactId>mockito-junit-jupiterartifactId>
       <version>3.7.7version>
       <scope>testscope>
   dependency>
   <dependency>
        <groupId>junitgroupId>
        <artifactId>junitartifactId>
        <version>4.13version>
        <scope>testscope>
    dependency>
   

2. 使用方式

   Mockito.mockStatic(Class mockClass)，如下：

   // 这里 DateUtil 内提供了静态方法
   MockedStatic<DateUtil> dateUtil = mockStatic(DateUtil.class);
   

   示例：

   import static org.mockito.Mockito.mockStatic;
   
   @RunWith(MockitoJUnitRunner.class)
   public class AlphaServiceTest {
   
       @Test
       public void testHttp() {
           ...
           
           MockedStatic<HTTPClient> httpClient = mockStatic(HTTPClient.class);
           httpClient.when(() -> HTTPClient.sendPost("xxx/zzz/ccc", "hello")).thenReturn("success");
           
           ...
           
           // 关闭
           httpClient.close();
       }
       
   

   这样基本上就 OK 了。唯一需要注意下的就是 httpClient.close()，这个问题会在「3.其他」中 “错误提示 static mocking is already registered in the current thread To create a new mock, the existing static mock registration must be deregistered” 进行详细说明）

3. 其他

   • 如果项目中未引入 mockito-inline，会出现如下错误信息：

     org.mockito.exceptions.base.MockitoException: 
     The used MockMaker SubclassByteBuddyMockMaker does not support the creation of static mocks
     
     Mockito's inline mock maker supports static mocks based on the Instrumentation API.
     You can simply enable this mock mode, by placing the 'mockito-inline' artifact where you are currently using 'mockito-core'.
     Note that Mockito's inline mock maker is not supported on Android.
     
     	at com.annoroad.order.service.PreOrderServiceTestCase.testSaveClinicalFreeSuccess1(PreOrderServiceTestCase.java:86)
     	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.springframework.test.context.junit4.statements.RunBeforeTestExecutionCallbacks.evaluate(RunBeforeTestExecutionCallbacks.java:74)
     	at org.springframework.test.context.junit4.statements.RunAfterTestExecutionCallbacks.evaluate(RunAfterTestExecutionCallbacks.java:84)
     	at org.springframework.test.context.junit4.statements.RunBeforeTestMethodCallbacks.evaluate(RunBeforeTestMethodCallbacks.java:75)
     	at org.springframework.test.context.junit4.statements.RunAfterTestMethodCallbacks.evaluate(RunAfterTestMethodCallbacks.java:86)
     	at org.springframework.test.context.junit4.statements.SpringRepeat.evaluate(SpringRepeat.java:84)
     	at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325)
     	at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.runChild(SpringJUnit4ClassRunner.java:251)
     	at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.runChild(SpringJUnit4ClassRunner.java:97)
     	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$2.evaluate(ParentRunner.java:268)
     	at org.springframework.test.context.junit4.statements.RunBeforeTestClassCallbacks.evaluate(RunBeforeTestClassCallbacks.java:61)
     	at org.springframework.test.context.junit4.statements.RunAfterTestClassCallbacks.evaluate(RunAfterTestClassCallbacks.java:70)
     	at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
     	at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.run(SpringJUnit4ClassRunner.java:190)
     	at org.junit.runner.JUnitCore.run(JUnitCore.java:137)
     	at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:68)
     	at com.intellij.rt.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:33)
     	at com.intellij.rt.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:230)
     	at com.intellij.rt.junit.JUnitStarter.main(JUnitStarter.java:58)
     

   • 错误提示 static mocking is already registered in the current thread To create a new mock, the existing static mock registration must be deregistered

     当多个单元测试都使用了同一个 static mock 对象，且使用完成后都没有进行 close。此时，若这几个单元测试用一起执行，第一个单元测试占用了 static mock 对象，第二个单元测试就没有办法再占用了。

     如果出现了这种情况，解决办法也很简单，就是关闭 static mock 对象，如下：

     import static org.mockito.Mockito.mockStatic;
     
     @RunWith(MockitoJUnitRunner.class)
     public class AlphaServiceTest {
     
         @Test
         public void testHttp1() {
             ...
             
             MockedStatic<HTTPClient> httpClient = mockStatic(HTTPClient.class);
             httpClient.when(() -> HTTPClient.sendPost("xxx/zzz/ccc", "hello")).thenReturn("success");
             
             ...
     
     		httpClient.close();
         }
         
         @Test
         public void testHttp2() {
             ...
             
             MockedStatic<HTTPClient> httpClient = mockStatic(HTTPClient.class);
             httpClient.when(() -> HTTPClient.sendPost("xxx/zzz/ccc", "hello")).thenReturn("success");
             
             ...
     
     		httpClient.close();
         }
         
         @Test
         public void testHttp3() {
             ...
             
             MockedStatic<HTTPClient> httpClient = mockStatic(HTTPClient.class);
             httpClient.when(() -> HTTPClient.sendPost("xxx/zzz/ccc", "hello")).thenReturn("success");
             
             ...
     		
     		httpClient.close();
         }
     

     如果你的很多单元测试中都用到了 mockStatic(HTTPClient.class)，且觉得在每个单元测试当中都写一遍 mockStatic()…close() 很低效，可以采用下边的方式：

     import static org.mockito.Mockito.mockStatic;
     
     @RunWith(MockitoJUnitRunner.class)
     public class AlphaServiceTest {
     	private MockedStatic<HttpClietn> httpClient;
     
     	// 每个单元测试启动前，先执行该方法（高版本中 @Before 被替换成 @BeforeEach）
         @Before
         public void setUp() {
             this.httpClient = mockStatic(HTTPClient.class);
         }
         
     	// 每个单元测试执行完成后，执行该方法（高版本中 @After 被替换成 @AfterEach）
         @After
         public void teardown() {
             this.httpClient.close();
         }
     
         @Test
         public void testHttp1() {
             ...
             
             httpClient.when(() -> HTTPClient.sendPost("xxx/zzz/ccc", "hello")).thenReturn("success");
             
             ...
         }
         
         @Test
         public void testHttp2() {
             ...
             
             httpClient.when(() -> HTTPClient.sendPost("xxx/zzz/ccc", "hello")).thenReturn("success");
             
             ...
         }
         
         @Test
         public void testHttp3() {
             ...
             
             httpClient.when(() -> HTTPClient.sendPost("xxx/zzz/ccc", "hello")).thenReturn("success");
             
             ...
         }
     

     这样就清爽多了 ~：）