What is the legal test for qualified testimony in a civil case?

"[A] trial court judgment is ordinarily presumed to be correct and the burden is on an appellant to demonstrate, on the basis of the record presented to the appellate court, that the trial court committed an error that justifies reversal of the judgment." (Jameson v. Desta (2018) 5 Cal.5th 594, 608-609.) A.G. did not meet that burden.

"A person is qualified to testify as an expert if he has special knowledge, skill, experience, training, or education sufficient to qualify him as an expert on the subject to which his testimony relates." (Evid. Code, 720, subd. (a).) "When a preliminary showing is made that the proposed witness has sufficient knowledge to qualify as an expert under the Evidence Code, questions about the depth or scope of his or her knowledge or experience go to the weight, not the admissibility, of the witness's testimony." (People v. Jones (2013) 57 Cal.4th 899, 949-950.) The test is whether it is likely the witness has sufficient knowledge, skill or experience to assist the fact finder.

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(Wegner et al, Cal. Practice Guide: Civil Trials and Evidence (The Rutter Group 2016) 8:733, p. 8C-129.)