What is the test for certifying an expert to give an opinion in a medical malpractice case?

We start with the general principle that the competency and qualification of an expert to give his opinion is within the sound discretion of the trial judge. On appeal, that determination will not be disturbed unless a manifest abuse of discretion is shown. (Huffman v. Lindquist (1951) 37 Cal.2d 465, 476, 234 P.2d 34)