how early do you test?

Okay so been TTC since Sept- haven't told any friends or family that we're trying but then I randomly get this facebook message from someone I haven't spoken to in a while (below). Now I'm DYING to test!! Every other month I was fine with waiting until the day of and if AF was a no- show then I'd test (only once). So now here I am, AF due 12/24 and I'm absolutely going crazy! I wasn't so anxious the other times but ever since I got that message I can't stop thinking that I might be. I don't want to get my hopes up but it's hard!!
Sooooo when is too early to test?? Thinking maybe I can wait until tomorrow (12/21) ?! Thoughts???