What is the test for establishing a conflict of interest?

"When a court ' "knows or reasonably should know that a particular conflict exists," ' it should inquire into the conflict even in the absence of objection by the defendant or his or her counsel. [Citations.] . . . Although the trial court is required to perform some inquiry once it knows or reasonably should know of a particular conflict of interest, the court may decline to pursue the matter if, in its view, the potential for conflict is too slight." (People v. Cornwell (2005) 37 Cal.4th 50, 75, disapproved on other grounds in People v. Doolin, supra, 45 Cal.4th at p. 421 & fn. 22.)