Well but sometimes the line is really faint and also you can to some degree track how the pregnancy is progressing by testing over repeated days to see a progression in darkness. HCG, the hormone that they test for, is supposed to double every day. So especially if you’ve had losses in the past, it can be very reassuring to see a darker and darker line. Sometimes the test line will even pull die from the control line, those are called die stealers.