Opk question

So I have been taking opks for the last three cycles. I have never really gotten a positive (that I know of, I'm still new to opks). Well on December 4th I took a opk (it was the third time I peed that morning) and about five seconds after I stuck it in the cup the test line came up really dark and it even dried that way! So does that definitely mean I ovulated? Or just a faulty test? Thanks!