Can someone tell me what is this black line in test results

Ash
My periods is late by 2 days.I believe its late since I ovulated late, but was curious to take a pregnancy test. When I took the test it was negative but I noticed an inverted L shape black line in the test. Can someone tell me what is this line? Do u get this sort of line in all pregnancy tests?? Do we have to take easy@home pregnancy test only in the mornings to see exact results?