"A friend is a person with whom I may be sincere. Before him I may think aloud."
- Ralph Waldo Emerson
This is one of the best quotes on friendship that I have come across. Most of the times we do so many things we don't like or say things we don't mean just to be agreeable and not go against the tide of commonly held beliefs and opinions.
If you really need to know who your true friends are then apply the above test. It will tell you how many true friends you have.