Regular COVID tests can detect the Delta variant, which means they can tell if you have the coronavirus or not. They can't tell which variant is involved, though. This would need genome sequencing, which is a separate technique from standard virus testing that not all labs can perform. Sequencing is a somewhat rare procedure that can cost up to $100 each test. Since the treatment is the same for any variant, it is not clinically useful to an individual patient to know whether the infection was caused by a variant or not.