If any breeder did any testing I would probably die of shock.
What testing should be done?
Annual ACVO or Cerf exam (eye exam)
OFA patellas
Cleared for liver shunt/MVD (easier said than done, but a normal ALT, fairly low bile acids - like under 40, no history of producing a shunt, ammonia tolerance test could also be done. Bile acids are not always on the ball for a Maltese, so precisely testing short of an invasive biopsy is a littler hard.)
Normal heart auscultation (for a Maltese, we are looking a PDA so the regular vet can do it although it would be nice if they had a cardiologist do it and register with OFA)
There is only one DNA marker test available for Maltese and it is for a glycogen storage disease. I don't know anyone who tests for it and to me, it isn't one of the biggies for the breed.
When somebody says a Maltese is DNA certified, that doesn't mean anything about their health. It just means a DNA sample was sent to the AKC so parentage can be established if need be. Popular sires are required to be on file.