PowerMockito mocking static method throws UnfinishedStubbingException

Question

I've been reading a lot about this error and I cannot find a solution.

This is my example code, you can copy it and launch it to reproduce the error.

Main class:

package example;

import org.junit.runner.RunWith;
import org.mockito.Matchers;
import org.mockito.Mockito;
import org.powermock.api.mockito.PowerMockito;
import org.powermock.core.classloader.annotations.PrepareForTest;
import org.powermock.modules.junit4.PowerMockRunner;

@RunWith(PowerMockRunner.class)
@PrepareForTest({ Utils.class, ClassA.class })
public class Test {

    @org.junit.Test
    public void test() {
        PowerMockito.mockStatic(Utils.class);
        Mockito.when(Utils.process(Matchers.anyString(), Matchers.anyString())).then(invocation -> {
            final String param1 = (String) invocation.getArguments()[0];
            final String param2 = (String) invocation.getArguments()[1];
            return myModifiedStaticMethod(param1, param2);
        });

        final ClassA classA = new ClassA();
        final ClassA classAMock = Mockito.mock(ClassA.class);
        Mockito.when(classAMock.doSomethingDB()).thenReturn(classA.doSomethingFile());

        classAMock.doSomethingDB();
    }

    private static Object myModifiedStaticMethod(String param1, String param2) {
        final String result = param1 + param2 + "modified!";
        System.out.println(result);
        return result;
    }
}

Class with static method:

package example;

public class Utils {

    public static Object process(String param1, String param2) {
        final String result = param1 + param2;
        System.out.println(result);
        return result;
    }
}

Class that uses the static method:

package example;

public class ClassA {

    public Object doSomethingFile() {
        System.out.println("hello! I'm doSomethingFile");
        return Utils.process("class", "a");
    }

    public Object doSomethingDB() {
        System.out.println("hello! I'm doSomethingDB");
        return "stuff";
    }
}

If you run this test the application will throw the next exception:

org.mockito.exceptions.misusing.UnfinishedStubbingException: 
Unfinished stubbing detected here:
-> at example.Test.test(Test.java:21)

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.core.MockGateway.doMethodCall(MockGateway.java:182)
    at org.powermock.core.MockGateway.doMethodCall(MockGateway.java:164)
    at org.powermock.core.MockGateway.methodCall(MockGateway.java:141)
    at example.Utils.process(Utils.java)
    at example.ClassA.doSomethingFile(ClassA.java:7)
    at example.Test.test(Test.java:21)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    at java.lang.reflect.Method.invoke(Unknown Source)
    at org.junit.internal.runners.TestMethod.invoke(TestMethod.java:68)
    at org.powermock.modules.junit4.internal.impl.PowerMockJUnit44RunnerDelegateImpl$PowerMockJUnit44MethodRunner.runTestMethod(PowerMockJUnit44RunnerDelegateImpl.java:326)
    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:310)
    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:298)
    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:218)
    at org.powermock.modules.junit4.internal.impl.PowerMockJUnit44RunnerDelegateImpl.runMethods(PowerMockJUnit44RunnerDelegateImpl.java:160)
    at org.powermock.modules.junit4.internal.impl.PowerMockJUnit44RunnerDelegateImpl$1.run(PowerMockJUnit44RunnerDelegateImpl.java:134)
    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:136)
    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:57)
    at org.powermock.modules.junit4.PowerMockRunner.run(PowerMockRunner.java:59)
    at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:89)
    at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:41)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:541)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:763)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:463)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:209)

This is an example based in my real application, of course it is more complicated than this, but it's based on the same scenario.

Ideas?, thanks!

Answer 1

Solution found! the issue is in this line:

Mockito.when(classAMock.doSomethingDB()).thenReturn(classA.doSomethingFile());

if I return an answer instead then it works:

Mockito.when(classAMock.doSomethingDB()).then(invocation -> classA.doSomethingFile());

Just in case there was someone working on this problem, thank you!