What I really do not understand (yes, all right, many things puzzle me) is that Trump seems to think that being tested every day makes him immune.
If you are tested it can only ever say either positive or negative. If it is positive, you have got the disease, and have probably had it for the best part of a week. The fact of being tested does not alter the fact of having, or not having, caught the disease.
It may make a difference to how soon you are treated for it, but that is all it can do.