如何模拟返回值为void的静态方法

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：


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);


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);