Yes. Twice.
Jessie (black and brown) is equal parts German Shepherd, Bull Mastiff, Airedale Terrier, and dunno-what.
Zoe (white) is 3/4 Chihuahua and 1/8 West Highland White Terrier.
Are these tests medically useful? Perhaps. The science is still evolving. There isn’t a lot of information available to veterinarians yet regarding the accuracy and validity of the data, but reports do claim to find (or not find) markers that may indicate susceptibility to certain diseases. Reports also vary between DNA testing companies.
I do have an answer when people ask me what breed they are.