Personally, I tested on the very first day of my missed period and got a faint line. It is always better to wait till your period date to avoid confusion.
I tested three days after my missed period and got a dark line. Based on my experience, testing too early just causes unnecessary stress, so give it a few days.
I waited till 2 days after my missed period to test. My doctor had only allowed very gentle walking till we confirmed the pregnancy, so I didn't want to rush into any heavy yoga before knowing for sure.
I know how agonizing the wait is, my heart was racing when I tested! Even if you test early and get a negative, don't lose hope and try again in a few days.