Powermock: Static interface method gives unfinished stubbing exception

Question

I want to mock a static interface method with Powermock. Here's the interface:

public interface IConcurrentUtil {
    static void threadSleep(final long millis) {
        try {
            Thread.sleep(millis);
        } catch (final InterruptedException e) {
            ;
        }
    }
}

Here's the class which uses threadSleep:

public class ConcurrentUser {

    public void callInterfaceMethod() {
        IConcurrentUtil.threadSleep(3000L);
    }
}

And finally the test class:

@RunWith(PowerMockRunner.class)
@PrepareForTest(ConcurrentUser.class)
@PowerMockIgnore("javax.management.*")
public class ConcurrentUtilsTest {

    private ConcurrentUser concurrentUser;

    @Before
    public void setUp() {
        concurrentUser = new ConcurrentUser();
    }

    @Test
    public void testThreadSleepCallsSleepCorrect() throws Exception {
        mockStatic(IConcurrentUtil.class);
        doNothing().when(IConcurrentUtil.class);
        IConcurrentUtil.threadSleep(3000L);

        concurrentUser.callInterfaceMethod();

        verifyStatic(times(1));
        IConcurrentUtil.threadSleep(3000L);
    }
}

Powermock gives this error:

org.mockito.exceptions.misusing.UnfinishedStubbingException: 
Unfinished stubbing detected here:
-> at org.powermock.api.mockito.internal.PowerMockitoCore.doAnswer(PowerMockitoCore.java:36)

E.g. thenReturn() may be missing.
Examples of correct stubbing:
    when(mock.isOk()).thenReturn(true);
    when(mock.isOk()).thenThrow(exception);
    doThrow(exception).when(mock).someVoidMethod();
Hints:
 1. missing thenReturn()
 2. you are trying to stub a final method, you naughty developer!
 3: you are stubbing the behaviour of another mock inside before 'thenReturn' instruction if completed

    at org.powermock.api.mockito.PowerMockito.verifyStatic(PowerMockito.java:288)
    at com.test.concurrent.ConcurrentUtilsTest.testThreadSleepCallsSleepCorrect(ConcurrentUtilsTest.java:35)
    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:483)
    at org.junit.internal.runners.TestMethod.invoke(TestMethod.java:68)
    at org.powermock.modules.junit4.internal.impl.PowerMockJUnit44RunnerDelegateImpl$PowerMockJUnit44MethodRunner.runTestMethod(PowerMockJUnit44RunnerDelegateImpl.java:310)
    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:294)
    at org.powermock.modules.junit4.internal.impl.PowerMockJUnit47RunnerDelegateImpl$PowerMockJUnit47MethodRunner.executeTestInSuper(PowerMockJUnit47RunnerDelegateImpl.java:127)
    at org.powermock.modules.junit4.internal.impl.PowerMockJUnit47RunnerDelegateImpl$PowerMockJUnit47MethodRunner.executeTest(PowerMockJUnit47RunnerDelegateImpl.java:82)
    at org.powermock.modules.junit4.internal.impl.PowerMockJUnit44RunnerDelegateImpl$PowerMockJUnit44MethodRunner.runBeforesThenTestThenAfters(PowerMockJUnit44RunnerDelegateImpl.java:282)
    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:207)
    at org.powermock.modules.junit4.internal.impl.PowerMockJUnit44RunnerDelegateImpl.runMethods(PowerMockJUnit44RunnerDelegateImpl.java:146)
    at org.powermock.modules.junit4.internal.impl.PowerMockJUnit44RunnerDelegateImpl$1.run(PowerMockJUnit44RunnerDelegateImpl.java:120)
    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:122)
    at org.powermock.modules.junit4.common.internal.impl.JUnit4TestSuiteChunkerImpl.run(JUnit4TestSuiteChunkerImpl.java:106)
    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.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:50)
    at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:459)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:675)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:382)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:192)

I'm using PowerMock 1.6.2 and JUnit 4.12.

Are there any special rules or commands which need to be applied when dealing with static(or default) interface methods?

score 4 · Accepted Answer · edited May 23 '17 at 12:02

Actually in your case, you do not need to do stubbing, as mockStatic already does this for you, it's just redundant.

So, the following would work:

@RunWith(PowerMockRunner.class)
@PrepareForTest(IConcurrentUtil.class)
@PowerMockIgnore("javax.management.*")
public class ConcurrentUtilTest {

    private ConcurrentUser concurrentUser;

    @Before
    public void setUp() {
        concurrentUser = new ConcurrentUser();
    }

    @Test
    public void testThreadSleepCallsSleepCorrect() throws Exception {
        PowerMockito.mockStatic(IConcurrentUtil.class);

        concurrentUser.callInterfaceMethod();

        PowerMockito.verifyStatic(Mockito.times(1));
        IConcurrentUtil.threadSleep(3000L);
    }
}

But in case you really do want to do some stubbing, here is an example that works with the versions you're using:

PowerMockito.mockStatic(FileUtils.class, Answers.CALLS_REAL_METHODS.get());
PowerMockito.doThrow(new IOException()).when(FileUtils.class, "copyFile", any(File.class), any(File.class));

Here, I am using the 2-args mockStatic signature because I want to do partial stubbing: real methods are called on the FileUtils class unless I stub it, as I do in the second line. You could use the 1-arg version as well if you don't mind all static methods being stubbed with the default answer.

You can also have a look at this answer and this one.

Thanks for your answer, but how do I need to alter testThreadSleepCallsSleepCorrect to get rid of the error message? — Juergen, Jul 14 '15 at 15:49
@johnmartel The workaround is good. But what If I really want to stub an Interface method? When I tried doing this, I got the same exception. After I changed the interface to a class, the stubbing went through fine. Is this a known limitation? — Dhiraj, Jul 17 '15 at 08:24
It seems indeed to be a limitation. Our friend @juxeii who first asked this question has opened an issue in PowerMock: https://code.google.com/p/powermock/issues/detail?id=550. See here for an interesting discussion on the static interface methods added in Java 8: http://programmers.stackexchange.com/questions/233053/why-were-default-and-static-methods-added-to-interfaces-in-java-8-when-we-alread — johnmartel, Jul 18 '15 at 00:04
Seems that `Answers.CALLS_REAL_METHODS.get()`do the job. Without it I always got `UnfinishedStubbingException`, even with the correct `doThrow()`. — , Dec 01 '16 at 21:37

Powermock: Static interface method gives unfinished stubbing exception

1 Answers1