title: The right way to test rxjs
body: <p>I brought the book <em>"rxjs in action"</em> and just finish the testing section.</p>
  
  <p>Testing rxjs codes are different then usual testing, because everything are lazy loading. </p>
  
  <p>In the book, they mention two test method, either passing done(I am using QUnit and done signals async code is finish) or marble diagrams.   </p>
  
  <p>My question is, which method should I choose, that I have mentioned above? </p>