One of the many idioms using the word pass, pass muster means to attain approval or meet a set of expectations. The verb may be conjugated through all its forms. There is no plural for muster.
The word pass could mean this all on its own (e.g., I passed!), but the idiom has a more nuance.
Muster is a military term for the act of gathering a troop together, specifically for the soldiers to be inspected.
So, passing muster can be understood to mean achieving a rigorous set of expectations, usually from a third party judge.
Cuomo, who controls the MTA, has described it as “bloated,” which implies that he will expect significant cuts in order for it to pass muster in the Legislature this summer. [Minneapolis Star Tribune]
Whether it passes muster remains to be seen but the fact that Greek banks would have collapsed by the middle of this week without a deal suggests even if the first iteration falls short, it will meet euro zone demands soon after. [Reuters]
Members of the Wausau School Board zeroed in on two building options they believe have the best chance of passing muster among district voters in an April referendum, neither of which involves building a new school. [Wausau Daily Herald]
But it appears the original ending to The Casual Vacancy has not passed muster under the high standards of television. The BBC has changed the final scenes of the novel, it has been disclosed, after screenwriters found it was too “grim” for Sunday night television. [The Telegraph]