What is the test for admitting or excluding evidence in a civil case?

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.]' [Citations.] The trial court's exercise of discretion in admitting the evidence is reviewed on appeal for abuse of discretion." (People v. Catlin (2001) 26 Cal.4th 81, 134.)