回看三年前的一篇日志 Mockito 3.4.0 开始可 Mock 静态方法，最后对 Mockito 产生的缺憾是它无法用来 Mock 非测试线程(主线程)中的静态方法调用。其实这也是可以变通的，下面慢慢道来。
首先回顾一下 Mockito 的静态方法 Mock 的使用方法，随着 Mockito 版本的升级，引入依赖的方式也发生了些许的变化，以 Maven 项目为例，如果在 JUnit 5 下用 Mockito 的 pom.xml 依赖中为
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<dependency> <groupId>org.mockito</groupId> <artifactId>mockito-junit-jupiter</artifactId> <version>5.14.1</version> <scope>test</scope> </dependency> |
由它引入的全部相关依赖
如今不再使用 mockito-inline 依赖了，以及它的 mockito-extensions/org.mockito.plugins.MockMaker(mock-make-inline) 和 mockito-extensions/org.mockito.plugins.MemberAccessor(memer-accessor-module)。
测试代码
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public class MockitoDemoTest { @Test public void testMockitoMockStatic() { LocalDate yearOf1970 = LocalDate.of(1970, 1, 1); try (MockedStatic<LocalDate> theMock = Mockito.mockStatic(LocalDate.class)) { theMock.when(() -> LocalDate.of(anyInt(), anyInt(), anyInt())).thenReturn(yearOf1970); LocalDate localDate = LocalDate.of(2024, 10, 10); assertEquals(1970, localDate.getYear()); // Ok } } } |
Mock 了静态方法 LocalDate.of(year, month, day), 所以在 try(MockedStatic) 块中无论传入什么参数给 LocalDate.of() 方法返回的都是 1970-01-01
try(MockedStatic) 块只对它所在的线程起作用，如果 LocalDate.of() 是在其他线程中调用就无能为力了。
比如用下方的代码演示非主线程(测试线程)中调用 LocalDate.of()时不能被 Mock 的效果
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public class MockitoDemoTest { @Test public void testMockitoMockStatic() { LocalDate yearOf1970 = LocalDate.of(1970, 1, 1); try (MockedStatic<LocalDate> theMock = Mockito.mockStatic(LocalDate.class)) { theMock.when(() -> LocalDate.of(anyInt(), anyInt(), anyInt())).thenReturn(yearOf1970); AtomicReference<LocalDate> localDateRef = new AtomicReference<>(); Thread thread = new Thread(() -> localDateRef.set(LocalDate.of(2024, 10, 10))); thread.start(); thread.join(); assertEquals(1970, localDateRef.get().getYear()); // Failed } catch (InterruptedException e) { throw new RuntimeException(e); } } } |
这个测试就会失败了
MockitoDemoTest.testMockitoMockStatic:49 expected: <1970> but was: <2024>
不过实际应用中我们多用线程池，不是说 try(MockedStatic) 只对它所在的线程起作用吗，那么我们可以对线程池来个腾龙换鸟，把主线程作为线程池中的唯一线程，这样所有的代码都会在 try(MockedStatic) 所在的线程(主线程)中执行了。
为演示全过程，先创建一个待测试的类 MockitoDemo
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public class MockitoDemo { private ExecutorService threadPool; public MockitoDemo(ExecutorService threadPool) { this.threadPool = threadPool; } public LocalDate getLocalDate() { Future<LocalDate> future = threadPool.submit(() -> LocalDate.of(2024, 10, 10)); try { return future.get(); } catch (Exception e) { throw new RuntimeException(e); } } } |
如果不管不顾线程池的角色，写如下的测试代码
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public class MockitoDemoTest { @Test public void testMockitoMockStatic() { MockitoDemo mockitoDemo = new MockitoDemo(Executors.newFixedThreadPool(2)); LocalDate yearOf1970 = LocalDate.of(1970, 1, 1); try (MockedStatic<LocalDate> theMock = Mockito.mockStatic(LocalDate.class)) { theMock.when(() -> LocalDate.of(anyInt(), anyInt(), anyInt())).thenReturn(yearOf1970); LocalDate localDate = mockitoDemo.getLocalDate(); assertEquals(1970, localDate.getYear()); // Failed } } } |
测试也将无法通过
MockitoDemoTest.testMockitoMockStatic:46 expected: <1970> but was: <2024>
变通要来了，针对线程池下手，用当前线程作为唯一线程的线程池替代它就行，完整的实现是
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public class MockitoDemoTest { @Test public void testMockitoMockStatic() { ThreadPoolExecutor threadPool = new ThreadPoolExecutor(1, 1, 0, TimeUnit.SECONDS, new LinkedBlockingQueue<>()) { @Override public void execute(Runnable command) { command.run(); } }; MockitoDemo mockitoDemo = new MockitoDemo(threadPool); LocalDate yearOf1970 = LocalDate.of(1970, 1, 1); try (MockedStatic<LocalDate> theMock = Mockito.mockStatic(LocalDate.class)) { theMock.when(() -> LocalDate.of(anyInt(), anyInt(), anyInt())).thenReturn(yearOf1970); LocalDate localDate = mockitoDemo.getLocalDate(); assertEquals(1970, localDate.getYear()); // Ok } } } |
测试通过
主要的行为就是覆盖了 execute(Runnable command) 方法，直接执行 command.run(), 所起的作用就是提交到 threadPool 的任务全部直接调用创建该 threadPool 实例的线程去执行，即实现了一个只有主线程(测试线程)的线程池，从而使得 try(MockedStatic) 与 MockitoDemo.getLocalDate() 中的 LocalDate.of(2024, 10, 10) 由同一个线程执行。
话外
Maven 中使用当前的 Mockito 5.14.1 版本时，运行 mvn test 会看到如下控制台输出
Mockito is currently self-attaching to enable the inline-mock-maker. This will no longer work in future releases of the JDK. Please add Mockito as an agent to your build what is described in Mockito's documentation: https://javadoc.io/doc/org.mockito/mockito-core/latest/org/mockito/Mockito.html#0.3
此篇测试用的 JDK 版本为 21, 参考信息所指引的链接 https://javadoc.io/doc/org.mockito/mockito-core/latest/org/mockito/Mockito.html#0.3，在 pom.xml 中加上
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<plugin> <groupId>org.apache.maven.plugins</groupId> <artifactId>maven-dependency-plugin</artifactId> <executions> <execution> <goals> <goal>properties</goal> </goals> </execution> </executions> </plugin> <plugin> <groupId>org.apache.maven.plugins</groupId> <artifactId>maven-surefire-plugin</artifactId> <configuration> <argLine>@{argLine} -javaagent:${org.mockito:mockito-core:jar}</argLine> </configuration> </plugin> |
再次运行 mvn test, 提示信息便消失了。
