What is the test for revoking probation and imposing a prison term on a defendant who has breached the terms and conditions of probation?

(1) A court may not revoke probation unless the evidence supports "a conclusion [that] the probationer's conduct constituted a willful violation of the terms and conditions of probation." (People v. Galvan (2007) 155 Cal.App.4th 978, 982 [66 Cal.Rptr.3d 426].) Where a probationer is unable to comply with a probation condition because of circumstances beyond his or her control and defendant's conduct was not contumacious, revoking probation and imposing a prison term are reversible error. (People v. Zaring (1992) 8 Cal.App.4th 362, 379 [10 Cal.Rptr.2d 263].)