What is the test for a defendant's right to retain counsel of his own choosing?

"The right to the effective assistance of counsel 'encompasses the right to retain counsel of one's own choosing. [Citations.]' [Citation.] Underlying this right is the premise that 'chosen representation is the preferred representation. Defendant's confidence in his lawyer is vital to his defense. His right to decide for himself who best can conduct the case must be respected wherever feasible.' " (People v. Courts (1985) 37 Cal.3d 784, 789 (Courts).) The unjustified deprivation of counsel of the defendant's choice is a structural error requiring reversal, and is not subject to harmless error analysis. (United States v. Gonzalez-Lopez (2006) 548 U.S. 140, 149-150.)