How can I test if my son is gay?

Just leave him be.

You only have on job as a parent, to love you child unconditionally. Do that.

He gets it from his dad.         Test dad.               

Perhaps try interacting with him once in a while lol

You could... ask him?

Make a big clay volcano, fill it with baking soda, and then pour some vinegar into the top of the volcano.

And if - while this is all erupting - your son is busysucking a dick, he’s gay, hun.

Couldn't you just ask him?

Kissing another boy.

You can’t. Just make him feel comfortable talking to you and he’ll tell you when the time is right. 

Tell him to drop his pants. Spread his butt cheeks. When a yahoo employee licks his anus, see if he enjoys it or not. If he likes it, he’s gay. If he doesn’t, he’s not gay. 

Crack out the litmus paper.