Speaking about friendship is something really difficult because it forces to get into the people experiences. For example in my case, my first friends were my cousins because I grew up with them, in consequence, we had shared lots of experiences, specially mischiefs. But not always friendship is about that, some people still retains friends of their childhood, of that of live when school becomes the most important thong in the entire world because the friends you love and spend time.
I think it is also important to say that friendship as most of human relationships needs to be cultivated in time. However time is the best TEST TO MEASURE FRIENDSHIP.