A long ( and I mean looooooong) time ago my friend and I have discussed this. And we have come to this: when you call your friend and ask to meet you in the woods... at 3 a.m. ... with an axe... and possibly a showel... no questions asked. And they come. This is when you know. :)
Ever since when we need each other and we meet at some urgency we say "here I am with my axe".
A private joke, of course. But the point is you know the true friend when you need him and he's there. No unnecessary questiunnecessaryAnd no metter how idiotic your request sounds. The true friend is always there.