What is the legal test for reinstating probation for a defendant who has breached probation but has not been sentenced to prison?

"We review a probation revocation decision pursuant to the substantial evidence standard of review [citation], and great deference is accorded the trial court's decision, bearing in mind that '[p]robation is not a matter of right but an act of clemency, the granting and revocation of which are entirely within the sound discretion of the trial court.' [Citations.]" (People v. Urke (2011) 197 Cal.App.4th 766, 773.)

"When the initial sentencing court imposes a state prison sentence but stays execution of the sentencing pending completion of probation, on a subsequent violation of probation the court does not have discretion to change the previously indicated sentence. [Citation.] The court does have discretion to reinstate probation. [Citation.] Reinstatement of probation, however, requires a determination by the trial court that the interests of justice so require. [Citation.] What the interests of justice require in a particular case constitutes a question uniquely addressed to the broad judicial discretion of the trial court." (People v. Stuckey (2009) 175 Cal.App.4th 898, 916; see People v. Medina (2001) 89 Cal.App.4th 318, 321-322.)