How to send text messages to test how much she likes herself?

First of all, I'm not a brother. If you really want to try, just send a text message to tell her, "I heard that your boyfriend is XXX." See if she is eager to explain everything to you. If so, there is a 90% chance that she likes it, but I advise you not to try it, because emotional things can't be used. If you like it, tell her generously that it doesn't matter whether she likes you or not, because not all happy feelings belong to two of a kind from the beginning. If you like it, pursue it boldly. I wish you success!