What is the legal test for corroborating testimony of an accomplice in a criminal case?

The testimony of an accomplice must be corroborated before a conviction can be based thereon.⁴⁶ (People v. Slaughter (2002) 27 Cal.4th 1187, 1203, disapproved on another ground in People v. Diaz (2015) 60 Cal.4th 1176, 1189-1190.) "Testimony" in this regard includes all oral statements made by a coconspirator or an accomplice under oath in a court proceeding, and all out-of-court statements of such persons that are made under suspect circumstances such as police questioning and used as substantive evidence of guilt. (People v. Williams (1997) 16 Cal.4th 153, 245.) The requirement is a statutory, not a federal constitutional, one. (Sattiewhite, supra, 59 Cal.4th at p. 473.)