How can I test....? (Ladies preferred, Gents you are welcome to answer)?

I would say that if a girl really like you then she would laugh at a lot of your jokes. And if she texts then she'll probably text you 24/7 (or very close) If she seems to always hang out with you or sit by you then she probably is interested. If you text her then you could make a joke about her being the person you text the most and if she says that she texts you the most too then thats another sign.