在编写代码时，经常需要调用别人已经写好的工具类方法，而这些方法经常又是使用静态方法实现的。而我们在测试自己的代码时，又不想真正执行这些方法，此时就需要对这些静态方法进行mock。在如何使用Powermock对静态方法进行mock文章中，我们介绍了如何对带有返回值的方法进行mock。那么对于返回值为void的方法如何模拟呢？
同样的，我们先看下待测试类：
public class Utility {
public static void doSomething(String var) {
throw new UnsupportedOperationException();
}
}
public class UtilityHelper {
public void call() {
Utility.doSomething("test");
}
}
1、不做任何方法模拟
我们先不mock该静态方法，看下效果：
@RunWith(PowerMockRunner.class)
@PrepareForTest({Utility.class})
public class UtilityHelperTest {
private UtilityHelper utilityHelper;
@Test(expected = UnsupportedOperationException.class)
public void testCall() throws Exception {
utilityHelper = new UtilityHelper();
utilityHelper.call();
}
}
执行该测试方法，会返回UnsupportedOperationException，正好和我们期望的结果相同，所以该测试用例执行正确。
2、模拟静态类
下面我们加一行代码，再看看效果：
@RunWith(PowerMockRunner.class)
@PrepareForTest({Utility.class})
public class UtilityHelperTest {
private UtilityHelper utilityHelper;
@Test(expected = UnsupportedOperationException.class)
public void testCall() throws Exception {
PowerMockito.mockStatic(Utility.class);
utilityHelper = new UtilityHelper();
utilityHelper.call();
}
}
由于我们加了一行对Utility类进行mock的语句，导致Utility里面的所有方法都不会被真正执行，此时调用doSomething方法时不会抛出UnsupportedOperationException，该测试方法执行错误。
java.lang.AssertionError: Expected exception: java.lang.UnsupportedOperationException
at org.powermock.modules.junit4.internal.impl.PowerMockJUnit44RunnerDelegateImpl$PowerMockJUnit44MethodRunner.runTestMethod(PowerMockJUnit44RunnerDelegateImpl.java:318)
at org.junit.internal.runners.MethodRoadie$2.run(MethodRoadie.java:89)
at org.junit.internal.runners.MethodRoadie.runBeforesThenTestThenAfters(MethodRoadie.java:97)
at org.powermock.modules.junit4.internal.impl.PowerMockJUnit44RunnerDelegateImpl$PowerMockJUnit44MethodRunner.executeTest(PowerMockJUnit44RunnerDelegateImpl.java:300)
at org.powermock.modules.junit4.internal.impl.PowerMockJUnit47RunnerDelegateImpl$PowerMockJUnit47MethodRunner.executeTestInSuper(PowerMockJUnit47RunnerDelegateImpl.java:131)
at org.powermock.modules.junit4.internal.impl.PowerMockJUnit47RunnerDelegateImpl$PowerMockJUnit47MethodRunner.access$100(PowerMockJUnit47RunnerDelegateImpl.java:59)
at org.powermock.modules.junit4.internal.impl.PowerMockJUnit47RunnerDelegateImpl$PowerMockJUnit47MethodRunner$TestExecutorStatement.evaluate(PowerMockJUnit47RunnerDelegateImpl.java:147)
at org.powermock.modules.junit4.internal.impl.PowerMockJUnit47RunnerDelegateImpl$PowerMockJUnit47MethodRunner.evaluateStatement(PowerMockJUnit47RunnerDelegateImpl.java:107)
at org.powermock.modules.junit4.internal.impl.PowerMockJUnit47RunnerDelegateImpl$PowerMockJUnit47MethodRunner.executeTest(PowerMockJUnit47RunnerDelegateImpl.java:82)
at org.powermock.modules.junit4.internal.impl.PowerMockJUnit44RunnerDelegateImpl$PowerMockJUnit44MethodRunner.runBeforesThenTestThenAfters(PowerMockJUnit44RunnerDelegateImpl.java:288)
at org.junit.internal.runners.MethodRoadie.runTest(MethodRoadie.java:87)
at org.junit.internal.runners.MethodRoadie.run(MethodRoadie.java:50)
at org.powermock.modules.junit4.internal.impl.PowerMockJUnit44RunnerDelegateImpl.invokeTestMethod(PowerMockJUnit44RunnerDelegateImpl.java:208)
at org.powermock.modules.junit4.internal.impl.PowerMockJUnit44RunnerDelegateImpl.runMethods(PowerMockJUnit44RunnerDelegateImpl.java:147)
at org.powermock.modules.junit4.internal.impl.PowerMockJUnit44RunnerDelegateImpl$1.run(PowerMockJUnit44RunnerDelegateImpl.java:121)
at org.junit.internal.runners.ClassRoadie.runUnprotected(ClassRoadie.java:34)
at org.junit.internal.runners.ClassRoadie.runProtected(ClassRoadie.java:44)
at org.powermock.modules.junit4.internal.impl.PowerMockJUnit44RunnerDelegateImpl.run(PowerMockJUnit44RunnerDelegateImpl.java:123)
at org.powermock.modules.junit4.common.internal.impl.JUnit4TestSuiteChunkerImpl.run(JUnit4TestSuiteChunkerImpl.java:121)
at org.powermock.modules.junit4.common.internal.impl.AbstractCommonPowerMockRunner.run(AbstractCommonPowerMockRunner.java:53)
at org.powermock.modules.junit4.PowerMockRunner.run(PowerMockRunner.java:59)
at org.junit.runner.JUnitCore.run(JUnitCore.java:137)
at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:68)
at com.intellij.rt.execution.junit.IdeaTestRunner$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)
Picked up JAVA_TOOL_OPTIONS: -Dfile.encoding=UTF-8
3、去掉@Test后面的expected验证
@RunWith(PowerMockRunner.class)
@PrepareForTest({Utility.class})
public class UtilityHelperTest {
private UtilityHelper utilityHelper;
@Test
public void testCall() throws Exception {
PowerMockito.mockStatic(Utility.class);
utilityHelper = new UtilityHelper();
utilityHelper.call();
}
}
此例中，由于我们去掉了expected这个期望验证结果，导致该测试方法目前没有任何验证存在，显然该用例执行正确。
4、加个 doSomething方法被调用的验证
没有任何验证的测试用例是无效的，下面我们在该用例中增加静态方法doSomething被调用的语句：
@RunWith(PowerMockRunner.class)
@PrepareForTest({Utility.class})
public class UtilityHelperTest {
private UtilityHelper utilityHelper;
@Test
public void testCall() throws Exception {
PowerMockito.mockStatic(Utility.class);
utilityHelper = new UtilityHelper();
utilityHelper.call();
PowerMockito.verifyStatic(Mockito.times(1));
Utility.doSomething(Mockito.any());
}
}
执行该测试用例，仍然执行正确，说明该静态方法确实是被调用了。此时我们可以看出，对于void类型的静态方法，我们不对该方法做任何的mock，仍然是执行正确的，这是因为mock整个类时，该类的所有方法就已经都被mock了，并且按照默认的方式进行处理，此时对于返回值为void的方法就是什么都不做。
5、显示对void方法进行mock
虽然不对void方法进行mock也能正常工作，但是我们还是习惯显示的对相应的方法进行mock，那么如何对void类型的方法进行mock呢？下面我们介绍两种写法：
- 方法一
PowerMockito.doNothing().when(Utility.class, "doSomething", Mockito.any());
此处采取的when原型如下：
<T> void when(Class<T> classMock, String methodToExpect, Object... parameters) throws Exception;
函数注释如下，可见该种方式主要适用于对私有静态且无返回值的方法进行mock。对私有静态方法且有返回值的可以参考使用Powermock对私有方法进行mock。
Allows to mock a static private method based on method name and parameters when stubbing in doThrow()|doAnswer()|doNothing()|doReturn() style
Example:
doThrow(new RuntimeException()).when(MyClass.class, "methodName", parameter1, parameter2);
- 方法二
PowerMockito.doNothing().when(Utility.class);
Utility.doSomething(Mockito.any());
此处采取的when原型如下：
void when(Class<?> classMock);
函数注释如下，可见该种方式主要适用于对公有静态且无返回值的方法进行mock。
Allows to choose a static method when stubbing in doThrow()|doAnswer()|doNothing()|doReturn() style
Example:
doThrow(new RuntimeException()).when(StaticList.class);
StaticList.clear();
综上所述，对于无返回值的静态方法，我们可以有两种方式实现mock:
1) 隐式写法，即只需要mock静态类即可；
2) 显示写法，此时需要根据方法是私有的还是公有的选择相应的格式；
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