When you are alone you may still test your distant visual acuity using the app and a mirror.
After setting the mirror toggle of the Snellen/ETDRS/Numbers Chart and the autoplay mode, you stand in front of a mirror, 1 meter away which effectively gives a 2-meter test distance. Then you put your phone/tablet near one of your ears with the screen facing the mirror. To ensure only one eye opened, you may cover the other eye with an “ eye patch”.
You should be able to use Tumbling E Chart, Landolt C Chart and HOTV Chart in front of a mirror naturally. For example, the E on the screen has limbs pointing right, and the E reflected in the mirror has limbs pointing left, you may swipe right on the screen to mark a correct answer, and this action is mirrored as swiping left in the mirror.