Unless you got 100 lbs or something, it's probably too expensive to have them tested (which can be done). Best bet is to boil up some DME, pitch a measured quantity of your mystery hops, and after a set time, try a taste. You could use some tested hops (same quantity, etc.) for a comparison.
Or, you could use them for flavor and aroma only, and use tested hops for bittering additions.
Finally, depending on the beer you could use the averages for that type and let it ride, knowing you may not hit a specific IBU target.
I normally choose door number three with my homegrown hops (since I make fairly few hop-focused beers) but it all depends what I'm brewing and to whom the beer is going.
