my fren bought a simple pregnancy tester using urine and was confused with the results. the image description shows that when two lines are shown in the tester, it means positive. but when it shows one line present then its negative. but what confuses us is that, does it usually means that the result always show two lines?? but with the two lines in d

ark colours means its positive. and when one of the two lines is lighter and the other darker, it means its negative??
she tried three brands with the same results. two lines present but the line at one end is darker and obvious while the other is fading.
has anyone ever tried these kinds of tester??