Positive or negitive test?

Ok so I took an equate pregnancy test from walmart. It was one of those plus or minus signs test. Plus if your pregnant minus if your not. Ok well when I first peed on it there was a plus sign and then I yelled for my husband told him I was pregnant not even a whole min. maybe 15-30 secs the plus sign disappeared. It was crazy to me. The plus sign never appeared after that. I mean if your not pregnant that plus sign should never appear at all, not even in the beginning right? So I am a little confused what to think about that test. What do you think?