Pregnancy tests and heat

I tested yesterday morning and the test line showed up very faint and only half of it was there. I could barely see it unless I looked close, but if you hold it up to the light you can see how half of it is there towards the left. Today after freaking out I realized the test had been sitting in the glove box of my car for a week or so, and the weather has been in the 70s and 80s for a few weeks. Could the test be considered defective because of the heat?