Dreams are your mind talking to itself. Your unconscious mind is not ruled by reason or logic as much as images and symbols.
Since everything in your dream is "you" (if you dream about your friend, its not your friend, its you....) you know what the meaning is of your dreams...since they are so subjectively about you.
So dreaming of a preganancy test is yourself maybe saying something is coming up? something youre expecting or not expecting is about to happen?
I dunno...you do though...