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

"The law requiring corroboration of accomplice testimony is well established." (People v. Rodrigues (1994) 8 Cal.4th 1060, 1128.) Section 1111 provides in part: "A conviction can not be had upon the testimony of an accomplice unless it be corroborated by such other evidence as shall tend to connect the defendant with the commission of the offense; and the corroboration is not sufficient if it merely shows the commission of the offense or the circumstances thereof."