All I will say is you will have more than three roosters out of 17.....
You will see soon enough!
I have had pretty good success with personality testing. It's not 100%, at least I don't rely on it 100%, but, so far, every chick that has tested having certain personality quirks has been a roo.
First, if you tap or scratch on their brooder, do they try to find the sound, peck at it, get a bit excited about it, or do they hang back, maybe just look that direction but not really investigate? The roos job is to be aware of it's surroundings and on alert for dangers to his flock at all times, and they tend to demonstrate that behavior early on. Sure, a hen could have that behavior but most of the time it's gonna be the roos.
Second, when you interact with the chicks, are there certain chicks that seem to want to interact with you? Do they trot over to your hand and peck you as if they are saying hey pay attention to me? Those are also going to tend to be roos. Another natural behavior of the roo is to establish the pecking order, especially among other roos. They eat first, they get the preferred roosting spot, and they lead the hens in and out of the coop. They will even select their favorite hens and maintain a separation between those hens and the other roos, so, when you are interacting with them the roos will kind of compete for your attention as if you are either the top hen, or you are the top roo and they are deferring to you, at least for now. At some point they may decide it's time to challenge you for that spot, but, at least while they are little they will just show defference and respect..
When choosing chicks I try to look for the disinterested ones that are kind of bunched together, and avoid the ones that get interested in my scratching at their brooder. I made the mistake of thinking chicks were just being friendly, that they liked me, if they trotted up to me when I tapped on the glass at Cal Ranch. Who can resist a little chick that stretches up at you when you reach your hand into their brooder? Certainly not me, but, every single one of them have been roos.
Today I made the mistake of not hand picking my second chick, and sure enough, it is showing signs of being a roo. It reared up at a bigger chick who was messing with it, instead of backing down and running away. Sigh, maybe it's just a feisty hen........maybe.
??? WHAT!!???? I was told I make no sense?
Roos are Cocky, pullets are pushy! SIMPLE!