What is the test for denial of a motion to replace an appointed attorney?

Defendant urges we must renew the matter de novo, relying on cases involving conflicts of interest in civil cases. We review the ruling for abuse of discretion. "'Denial of the motion is not an abuse of discretion unless the defendant has shown that a failure to replace the appointed attorney would "substantially impair" the defendant's right to assistance of counsel.'" (People v. Horton (1995) 11 Cal.4th 1068, 1102.) Defendant has not demonstrated an abuse of discretion.