PowerMockito mock single static method and return object

I want to mock a static method m1 from a class which contains 2 static methods, m1 and m2. And I want the method m1 to return an object.

I tried the following

PowerMockito.mockStatic(Static.class, new Answer<Long>() {

         @Override
         public Long answer(InvocationOnMock invocation) throws Throwable {
            return 1000l;
         }
      });

This is calling both m1 and m2, which has a different return type, so it gives a return type mismatch error.

2. PowerMockito.when(Static.m1(param1, param2)).thenReturn(1000l); But this is not called when m1 is executed.

3. PowerMockito.mockPartial(Static.class, "m1"); Gives compiler error that mockPartial not available, which I got from http://code.google.com/p/powermock/wiki/MockitoUsage.

What you want to do is a combination of part of 1 and all of 2.

You need to use the PowerMockito.mockStatic to enable static mocking for all static methods of a class. This means make it possible to stub them using the when-thenReturn syntax.

But the 2-argument overload of mockStatic you are using supplies a default strategy for what Mockito/PowerMock should do when you call a method you haven't explicitly stubbed on the mock instance.

From the javadoc:

> Creates class mock with a specified strategy for its answers to > interactions. It's quite advanced feature and typically you don't need > it to write decent tests. However it can be helpful when working with > legacy systems. It is the default answer so it will be used only when > you don't stub the method call.

The default default stubbing strategy is to just return null, 0 or false for object, number and boolean valued methods. By using the 2-arg overload, you're saying "No, no, no, by default use this Answer subclass' answer method to get a default value. It returns a Long, so if you have static methods which return something incompatible with Long, there is a problem.

Instead, use the 1-arg version of mockStatic to enable stubbing of static methods, then use when-thenReturn to specify what to do for a particular method. For example:

import static org.mockito.Mockito.*;

import org.junit.Test;
import org.junit.runner.RunWith;
import org.mockito.invocation.InvocationOnMock;
import org.mockito.stubbing.Answer;
import org.powermock.api.mockito.PowerMockito;
import org.powermock.core.classloader.annotations.PrepareForTest;
import org.powermock.modules.junit4.PowerMockRunner;

class ClassWithStatics {
  public static String getString() {
    return "String";
  }

  public static int getInt() {
    return 1;
  }
}

@RunWith(PowerMockRunner.class)
@PrepareForTest(ClassWithStatics.class)
public class StubJustOneStatic {
  @Test
  public void test() {
    PowerMockito.mockStatic(ClassWithStatics.class);

    when(ClassWithStatics.getString()).thenReturn("Hello!");

    System.out.println("String: " + ClassWithStatics.getString());
    System.out.println("Int: " + ClassWithStatics.getInt());
  }
}

The String-valued static method is stubbed to return "Hello!", while the int-valued static method uses the default stubbing, returning 0.