title: How to test back end from front end?
body: <p>Recently I've been asked this type of questions for several times.</p>
  
  <p>It is like "If you can't access the back end, how do you know if a problem is from front end or back end?", or "If you can't access the database, how do you know the performance issue in the website is from the front end or back end?", or "In front end, how can you differentiate if a problem is from front end or from back end?"</p>
  
  <p>I really don't have any clue how to answer this kind of questions. Can someone help me? Thanks in advance. </p>