You do nothing; your schoolmate's personal business is not your business. Unless you are this person's dear friend or you are personally interested in a relationship with this person, you have no right to pry.
There are no tests to see if your schoolmate is gay and it is none of your business and is a private matter. If you like your schoolmate it does not matter if they are gay or not and if you spread gossip about the possibility of them being gay you could cause many problems for that schoolmate so buckle down to your studies and forget testing your schoolmate. If they want you to know they will tell you.
there is no way finding out the orientation it may or may not be found in boys behaviour or in gestures .
It does not really matter if your schoolmate is gay or not and you are out of line by being curious about their private life. School is for learning and it is mature to accept people as they are if they are kind; loyal; giving individuals and being gay does not change it. Be wise and leave it alone and just accept this schoolmate as they are.
The eyes never lie. Watch if his eyes move when a man or woman enters the room. They are a dead giveaway.
Asking him is the ONLY way to tell. Or better yet, you can focus on your own life instead.
Just give yourself a self gay handjob and see if you like it.
to see if they smoke illegal things
No, don't test them. If they are your friends they hang out with you, talk to you, and do things with you~They already care about you.
like a test when you see how things are alike and different
if he knows you are gay then try to be good friends with him and see how it will go on from there if you think he is gay try talking to him and get him to talk about him to you and see if he is gay
they dont want to kill humans so they try it on animal to see if it is dangerous or not
To show the results of an experiment or test.