You can't go testing other people's dogs,
and if you buy him then have him tested what will you gain ? from that knowledge
except something to declare to your insurance company.
you are not buying a puppy from a KC breeder.
but yes from his photos which I can't make larger and from looking at my girls on my knee his nose is sort of ' normal '
Shih tzus are a Brachycephalic breed which means they suffer with little noses squished into their faces, french bull dogs esp suffer. but that is a whole different story.
I had a Japanese Chin, carefully chosen - I researched the breed / breeders and was allowed to buy him from his breeder ( a top show judge ) and my Vet upon seeing him for the first time commented ' he has good pair of nostrils ' well what else could she say as he basically didn't have a nose.
Luckily he never suffered from his breathing coz of his nose, it was heart failure that got him :(
My shih tzu didn't die due to breathing problems, I adopted her from a rescue at the age of 3, having fostered her for a year ( the ' right ' home never came along for her ) she died of a stoke aged 7.
Pugs are a Brachycephalic breed too.
Out of the 3 Brachycephalic dogs I currently have it is only the smaller Shih Tzu / Pug X that sometimes snorts or can suffer a bit in the heat. So clearly I don't walk my dogs during the day in the heat.