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

Penal Code section 1111 provides that "[a] conviction cannot 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." Where an accomplice testifies, the trial court must instruct the jury sua sponte that the accomplice's testimony is to be viewed with distrust and that the defendant cannot be convicted on the basis of the accomplice's testimony unless that testimony is corroborated. (People v. Zapien (1993) 4 Cal.4th 929, 982.)

"An accomplice is . . . defined as one who is liable to prosecution for the identical offense charged against the defendant on trial in the cause in which the testimony of the accomplice is given." (Pen. Code, 1111.) To be charged with the identical offense, the witness must be considered a principal under Penal Code section 31, which provides, "All persons concerned in the commission of a crime . . . whether they directly commit the act constituting the offense, or aid and abet in its commission, or, not being present, have advised and encouraged its commission." (See People v. Fauber (1992) 2 Cal.4th

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