What is the test for an expert testimony in a medical malpractice case?

Before a witness may testify as an expert, evidence must be presented to establish that he or she "has special knowledge, skill, experience, training, or education sufficient to qualify him [or her] as an expert on the subject to which his [or her] testimony relates." (Evid. Code, 720, subd. (a).) In addition, an expert witness's declaration is not admissible unless it discloses the matters relied upon in forming his or her opinion. (Kelley v. Trunk (1998) 66 Cal.App.4th 519, 524.)