What is the test for admitting evidence of prior criminal convictions to impeach the credibility of any witness?

Prior to any decision to admit evidence of felony convictions to impeach the credibility of any witness, the trial courts must give careful consideration to whether or not the evidence will be used by the trier of fact only for the purpose which justifies its admission. "(T)he true purpose of a criminal trial, the ascertainment of the facts . . . ," (People v. Riser (1956) 47 Cal.2d 566, 586, 305 P.2d 1, 13) is not advanced by the indiscriminate use of felony convictions which do not bear on the truthfulness of the witness' testimony. The danger inherent in the use of such prior felony convictions is that the jurors may disregard a witness' testimony because they disapprove of his felony convictions. The proper administration of justice and the search for truth cannot be advanced if jurors make decisions based on facts that are irrelevant to the issue before them.