What is a one-sentence summary of the following article?
It's about the people who are true behind your back. This section features some "tests" that you can make use of to observe and note how your friend behaves when you're not there to defend yourself. These tests are all optional, and you can try one, two or all of them, or just skip this section -- do whatever you feel most comfortable with. Ultimately, your feelings will matter most, so if needed, just jump to Part 3. This provides you with the opportunity to find out what type of people your friend hangs out with or if they say anything bad about you or one of your closer friends. Be around where they hang out and just be quietly in the background, saying nothing and not drawing attention to yourself, keeping a nice distance away. Don't give away any clues you're watching them, and if they're not being such a great friend, they probably won't even notice you. They might say uncomplimentary things about you, or about someone else who is really close to you. Listen for verbal clues, and watch for physical and emotional clues as well. A good and trustworthy friend won't gossip about you and won't spread rumors or, even worse, lies. Does your friend keep all of your confidences? Do you ever hear of anything you only told this friend being spoken of by someone else you didn't tell? Test your friend. Tell him or her a fake secret you have, and see if your friend makes rumors about the matter or not. Make sure that your fake secret is scandalous enough but does not involve anyone but you. This is entirely optional and if it feels icky, weird or undesirable, just skip it. If you think it might help and you have someone willing to help out, it can be one more thing to add to the mix for your decision-making. So, the test is: Have a classmate or coworker talk about you in an unflattering way to your friend, and have the classmate or coworker record or tell you whatever he or she said. If your classmate or coworker can't record the response, be the one to observe your friend while the unflattering scene unfolds. If your friend defends you, that's a great sign of loyalty but if he or she agrees and starts dissing you back, then you know this person isn't being a true friend.

Summary:
Remember that friendship is not about the people who are true to your face. Observe how your friend is when he or she doesn't notice you're about. Consider how your friend handles your confidences. Set up the trolling test.