Ovulation test.

Morgan • Married 4•20•2015 ☆ TTC #1 ☆ Currently on Cycle #30 ☆ Mommy to 4 wonderful fur babies
So I'm new to ovulation test strips, this is the first month I've used them. My temp is going up but the line on the tests is not getting any darker. Should they gradually get darker or just one day be dark?