doNothing method does not work with void static method

Question

I am assigned to add unit test code coverage to a 15 years old legacy project which is not using IoC and 0 unit test. I am not allowed to refactor the code since it works perfect fine on production, management does not want other teams get involved for refactoring such as QA testing, etc.

Service class has a performService method has following code

public void performService(requestMessage, responseMessage) {
        UserAccount userAccount = requestMessage.getUserAccount();
        GroupAccount groupAccount = requestMessage.getGroupAccount();
        Type type = requestMessage.getType();
        StaticServiceCall.enroll(userAccount, groupAccount, type);
        response.setStatus(Status.SUCCESS);
}

This StaticServiceCall.enroll method is calling remote service. My unit test is

@RunWith(PowerMockRunner.class)
@PrepareForTest(StaticServiceCall.class)
public class EnrollmentServiceTest {

@Test
public void testPerformService() {      
    mockStatic(StaticServiceCall.class);
    doNothing().when(StaticServiceCall.enroll(any(UserAccount.class), any(GroupAccount.class), any(Type.class)));
    service.performService(requestMessage, responseMessage);
    assertEquals("Enrollment should be success, but not", Status.SUCCESS, response.getStatus);
}

Eclipse complains with The method when(T) in the type Stubber is not applicable for the arguments (void)

Eclipse stops complain if test code change to

mockStatic(StaticServiceCall.class);
doNothing().when(StaticServiceCall.class);
StaticServiceCall.enroll(any(UserAccount.class), any(GroupAccount.class), any(Type.class));
service.performService(requestMessage, responseMessage);
assertEquals("Enrollment should be success, but not", Status.SUCCESS, response.getStatus);

Test case failed with UnfinishedStubbingException. I am using powermock 1.6.6

Answer 1

There is a misconception on your end. You think that you need to say that doNothing() should do nothing.

That is not necessary! As these lines

@PrepareForTest(StaticServiceCall.class) ... and 
mockStatic(StaticServiceCall.class);

are sufficient already.

You want to prevent the "real" content of that static method to run when the method is invoked during your test. And that is what mockStatic() is doing.

In other words: as soon as you use mockStatic() the complete implementation of the real class is wiped. You only need to use when/then/doReturn/doThrow in case you want to happen something else than nothing.

Meaning: just remove that whole doNothing() line!