title: Mockito / PowerMocktio doNothing for none void method
body: <p>I need a method which returns something to do nothing when invoked during testing, the class instance which owns the method is implemented as a spy. </p>
  
  <p>I am aware the doNothing() method only works with void methods. Is there a way to get the same  behaviour with a method that returns something? </p>
  
  <p>Thank you!</p>