What is the test for reasonable inference or speculation?

unreasonable inferences or speculation will not. " While substantial evidence may consist of inferences, such inferences must be "a product of logic and reason" and "must rest on the evidence" [citation]; inferences that are the result of mere speculation or conjecture cannot support a finding [citations.]. " ( Kasparian v. County of Los Angeles (1995) 38 Cal.App.4th 242, 260, 45 Cal.Rptr.2d 90 ; see People v. Morris (1988) 46 Cal.3d 1, 21, 249 Cal.Rptr. 119, 756 P.2d 843.)