What is the test for admitting character evidence in a criminal case?

Section 1101 prohibits the admission of character evidence, including evidence of prior, uncharged offenses, when offered to prove the defendant's commission of charged offenses. ( 1101, subd. (a).) The purpose of this prohibition "is to avoid placing the accused in a position of having to defend against crimes for which he has not been charged and to guard against the probability that evidence of other criminal acts having little bearing on the question whether defendant actually committed the crime charged would assume undue proportions and unnecessarily prejudice defendant in the minds of the jury, as well as [to] promote judicial efficiency by restricting proof of extraneous crimes." (People v. Kelley (1967) 66 Cal.2d 232, 238-239.)