What is the test for establishing the chain of custody of evidence in a criminal case?

altered, it is reasonably certain that there was no alteration. [] The requirement of reasonable certainty is not met when some vital link in the chain of possession is not accounted for, because then it is as likely as not that the evidence analyzed was not the evidence originally received. Left to such speculation the court must exclude the evidence. [Citations.] Conversely, when it is the barest speculation that there was tampering, it is proper to admit the evidence and let what doubt remains go to its weight." [Citations.]' " (People v. Catlin (2001) 26 Cal.4th 81, 134.) " 'While a perfect chain of custody is desirable, gaps will not result in the exclusion of the evidence, so long as the links offered connect the evidence with the case and raise no serious questions of tampering' " (Ibid.)

"[I]t is not the case, that anyone whose testimony may be relevant in establishing the chain of custody, authenticity of the sample, or accuracy of the testing device, must appear in person as part of the prosecution's case. [N]ot ... everyone who laid hands on the evidence must be called. '[G]aps in the chain [of custody] normally go to the weight of the evidence rather than its admissibility.' " (Melendez-Diaz v. Massachusetts (2009) 557 U.S. 305, 311, fn. 1.)