What is the test for a guilty plea in a criminal case?

waives any irregularity in the proceedings which would not preclude a conviction. [Citation.] Thus irregularities which could be cured, or which would not preclude subsequent proceedings to establish guilt, are waived and may not be asserted on appeal after a guilty plea. [Citation.] In other words, by pleading guilty the defendant admits that he [or she] did that which he [or she] is accused of doing and he [or she] thereby obviates the procedural necessity of establishing that he [or she] committed the crime charged. In short, a guilty plea 'admits all matters essential to the conviction.' " (People v. Turner (1985) 171 Cal.App.3d 116, 125-126, fn. omitted.) By entering a plea of no contest, defendant has waived any and all claims challenging his guilt. Moreover, in entering his plea, defendant waived his right to appeal other than sentencing error.