Mocking a singleton with mockito

Question

I need to test some legacy code, which uses a singleton in a a method call. The purpose of the test is to ensure that the clas sunder test makes a call to singletons method.

Answer 1

As a beginner in Software Development, IMO, dependency injection of a singleton class in a driver/otherservice is a good option. As we can control creation of a single instance of the class and still be able to mock the static methods (as you might have guessed, I have util services in my mind) without using something like PowerMock to mock the static methods (IME which was little painful) I am very much open to listen about it from experienced folks from SOLID or Good OO design principle perspective.

public class DriverSnapshotHandler {
    private FormatterService formatter;
    public DriverSnapshotHandler() {
        this(FormatterService.getInstance());
    }
    public DriverSnapshotHandler (FormatterService formatterService){
           this.formatter = formatterService;
    }
    public String getImageURL() {
        return FormatterService.getInstance().formatTachoIcon();
    }
}

and then test using Mockito, something like this.

@Test
public void testGetUrl(){
  FormatterService formatter = mock(FormatterService.class);
  when(formatter.formatTachoIcon()).thenReturn("TestURL");
  DriverSnapshotHandler handler = new DriverSnapshotHandler(formatter);
  assertEquals(handler.getImageURL(), "TestUrl";
}