How accurate are pregnancy tests?

Right, so I'm 13 days late for my period. My mother in law brought me a test 3 days ago, as I felt so tired unlike always. It came up positive. The line was literally bright red. According to my mother in law shes telling me the pregnancy tests always test wrong and its fake. I will be phoneing my doctor tomorrow for an oppointment, but I thought I'de share it with you ladies just to get it out my mind. How accurate are pregnancy tests?

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