What is the legal test for a treating physician's opinion in a medical malpractice case?

Courts "distinguish among the opinions of three types of physicians: (1) those who treat the claimant (treating physicians); (2) those who examine but do not treat the claimant (examining physicians); and (3) those who neither examine nor treat the claimant (non[-]examining physicians)." Lester v. Chater, 81 F.3d 821, 830 (9th Cir. 1995). Courts "afford greater weight to a treating physician's opinion because he is employed to cure and has a greater opportunity to know and observe the patient as an individual." Magallanes, 881 F.2d at 751 (internal quotations omitted); see e.g., Lester, 81 F.3d at 830 (stating that "more weight should be given to the opinion of a treating source than to the opinion of doctors who do not treat the claimant").