Hi. I have not had a candidiasis test, but I have been treated for it. Once with diflucan for 21 days, and later on (to "rule it out"), with swish/swallow nystatin. Neither of them had any effect on my symptoms. The 21 days of diflucan is apparently almost 100% effective, so the odds are that candidiasis was not my problem.
One PCP looked at the gunk on my tongue and said if it was candida, it would leave a sore or bleeding underneath it when scraped off.
I do still have gunk near the back of my tongue, but I think it's the normal flora of the mouth. They sell tongue scrapers for the masses because it's normal, not a sign of infection.
Depending on how my future appointments go (an endoscopy, then neurology), I may ask my PCP to have that stuff on my tongue cultured to see if there's anything bad in there. Even then, I'm not sure how they would treat it since we've already tried two of the main therapies.