Ok,
I have so many friends that are guys, (yes Im a girl) an they ask me this all the time. Mostly, the are all different situations but in this one I advise you to look at the girls point of view. How do you act towards her, knowing that you can ask yourself how she acts back. If your obviously flirty, and she is acting normal/flirty back, she probalby has a crush on you. If she starts acting a little weird or embarassed, that another sign. If shes acting normal, she might just want to be friends. then for the test, I would say help her. But also, you need to get to know her. make sure sh is not gay or something weird. Then figure out her birthday, and give her something specail so that she will know that you care for her. DO NOT USE A TEXT. All my friends HATE that. :) I think that you should say it in person. once your ready. or at least a note.
Good luck