title: Android - make activity use service mock
body: <p>In this thread it's explained how to mock android service:
  <a href="https://stackoverflow.com/questions/7583697/is-it-possible-to-mock-android-services-under-unit-tests">Is it possible to mock android services under unit tests?</a></p>
  
  <p>But how can I make my activity use this mock instead of real service?
  I'm not using any DI frameworks.</p>
  
  <p>Thanks!</p>