Mocking private methods used in public method with PowerMock, Mockito, and TestNG

Question

I want to write a unit test for a class I have. This class has a public method, and inside the public method there are calls to private methods in the same class. I want to mock the calls to those private methods. The class is similar to this:

public class SomeClass {
    public int somePublicMethod(int num) {
        int num2 = somePrivateMethod1(num);
        int num3 = somePrivateMethod2(num);

        return num2 + num3;
    }

    private int somePrivateMethod1(int num) {
        return 2*num;
    }

    private int somePrivateMethod2(int num) {
        return 3*num;
    }
}

For my unit test I am trying to use PowerMock with Mockito and TestNG. Here is my attempt at a test that tests somePublicMethod:

import static org.powermock.api.mockito.PowerMockito.doReturn;
import static org.powermock.api.mockito.PowerMockito.spy;

import org.powermock.core.classloader.annotations.PrepareForTest;
import org.testng.Assert;
import org.testng.annotations.Test;

@PrepareForTest(SomeClass.class)
public class SomeClassTest {

    @Test
    public void testSomePublicMethod() throws Exception {
        int num = 4;        

        SomeClass someClassSpy = spy(new SomeClass());

        doReturn(8).when(someClassSpy, "somePrivateMethod1", num);
        doReturn(12).when(someClassSpy, "somePrivateMethod2", num);

        int result = someClassSpy.somePublicMethod(num);

        Assert.assertEquals(result, 20);
    }
}

When I run this test I get an exception and some hints:

FAILED: testSomePublicMethod
org.mockito.exceptions.misusing.UnfinishedStubbingException: 
Unfinished stubbing detected here:
-> at org.powermock.api.mockito.internal.PowerMockitoCore.doAnswer(PowerMockitoCore.java:31)

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!

I've looked at some examples online but I haven't found one that uses PowerMock with Mockito and TestNG specifically to do what I want. Can someone give me some pointers on what I could do differently?

Answer 1

I don't think this is a problem with PowerMock. It looks like it should work just fine as is. I wonder if there is a problem with TestNG interacting with PowerMock?

I have no experience with TestNG, so I tried running the class in JUnit. SomeClass was left as is, SomeClassTest was minimally modified to use JUnit:

import static org.powermock.api.mockito.PowerMockito.*;

import org.junit.Assert;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.powermock.core.classloader.annotations.PrepareForTest;
import org.powermock.modules.junit4.PowerMockRunner;

@RunWith(PowerMockRunner.class)
@PrepareForTest(SomeClass.class)
public class SomeClassTest {

    @Test
    public void testSomePublicMethod() throws Exception {
        final int num = 4;

        final SomeClass someClassSpy = spy(new SomeClass());

        doReturn(8).when(someClassSpy, "somePrivateMethod1", num);
        doReturn(12).when(someClassSpy, "somePrivateMethod2", num);

        final int result = someClassSpy.somePublicMethod(num);

        Assert.assertEquals(result, 20);
    }
}

The test passes.

Do you need to specify a PowerMockRunner.class using @RunWIth or some similar annotation, as with JUnit? If I remove that annotation I recieve the same error message you posted.

EDIT:

According to this link: http://code.google.com/p/powermock/wiki/TestNG_usage

You need to tell TestNG to use the PowerMock object factory. To do this programmatically, add a method like this to your test class:

@ObjectFactory
public IObjectFactory getObjectFactory() {
    return new org.powermock.modules.testng.PowerMockObjectFactory();
}

or to be on the safe side you can also extend from the PowerMockTestCase:

@PrepareForTest(SomeClass.class)
public class SomeClassTest extends PowerMockTestCase {
   //...
}

Answer 2

You can't do by that way. Did you try to use reflection?

By using reflection, you can mock the private methods by mocking the invoke methods, or simpler: you can change it to public temporary, then after the test (maybe in the tearDown) - you can change it back to private.

Hope this help.

Answer 3

I think you are hiting a Mockito limit here. In similar cases, I use Powermock method replacement or, declare the target method as protected and override it when constructing the tested class instance. Hope that helps.