Not sure about the title but I can tell you that having a sense of smell is not a sign of being covid-negative. You can get 2 15-minute covid tests at walmart for 20 bucks
Not losing smell tells you almost nothing, especially since Omicron. Before that, even if it was frequent, most of the people with covid didn't have this symptom so it was only a weak indicator.
But speaking of reassurance, not losing taste and smell is great simply because you don't lose taste and smell. It is one of the most annoying "mild" covid symptoms. And severe cases are becoming less and less common.