Reverend Frank (Robin Williams, center) with Sadie (Mandy Moore) and Ben (John Krasinski) star in the romantic comedy License to Wed.

Warner Bros. / Peter Sorel Peter Sorel

A bride and groom find themselves at the mercy of a frenzied pastor who puts them through a rigorous series of unorthodox relationship tests before he’ll agree to perform the marriage in the zany romantic comedy License to Wed.

That the overly zealous clergyman (he even bugs their apartment to make sure they’re following his rule of no sex before the wedding) is played by Robin Williams and is a plus in making this outlandish, yet oddly predictable script work. Williams, lately saddled with downbeat dramas meant to prove that he can be a “serious actor,” is back at what he does best here — freewheeling comedy with snappy zingers and a mile-a-minute delivery.

His Reverend Frank (the denomination is a little hazy) is a sort of feel-good huckster whose sermons would play just as well on The Tonight Show. When first we see Rev. Frank, he’s teaching a catechism class about the Ten Commandments, using the kind of pop-up answer board on Family Feud.

“Good marriages are my business,” he promises Sadie Jones (Mandy Moore) and Ben Murphy (John Krasinski). But he also knows the pitfalls inherent in walking down the aisle. “Marriage is like sticking your tongue on a frozen flag pole,” he cautions as he sends Sadie and Ben on a series of obstacle-course tests to make sure they are devoted to each other and have faith in one another’s judgment. At one point he blindfolds Sadie behind the wheel of a car and sends her out into traffic with Ben giving her backseat driver instructions on how to maneuver the car.

Sometimes Reverend Frank’s relationship games seem downright mean spirited, such as the one where he has Ben and Sadie’s relatives assess one another with one-word descriptions, a recipe for disaster and hurt feelings. There’s a demented feeling to the character, abetted by the fact that Reverend Frank’s constant companion is a grimly self-serious young boy (Josh Flitter) in a black suit, who delights in the awkward situations Sadie and Ben find themselves in. The kid — Reverend Frank says he’s part of the Ministers of Tomorrow Project — seems like the acolyte from hell rather than heaven.

To gauge whether Sadie and Ben will be fit parents, Reverend Frank takes them to a hospital maternity ward to observe the traumas of childbirth, then gives them a pair of creepily lifelike twin robot dolls to see how they will cope with the day-to-day demands of parenthood.

One of the film’s funniest moments has Ben fiddling with the diapers on one of the robot dolls in a department store changing room, his fumbling efforts horrifying a mother at the next table who is changing her real infant’s diapers.

Ken Kwapis, who has directed many episodes of TV’s The Office as well as the 2005 teen-girl flick Sisterhood of the Traveling Pants, puts a breezy spin on License to Wed. Williams gets the lion’s share of funny lines and rolls with them. Moore makes a refreshingly easygoing bride-to-be while Krasinski, a 2002 Brown University grad who has a recurring role on The Office, becomes more and more frazzled as Reverend Frank’s trials grow loonier.

There’s a reason for all those difficult trials as well as a message, which becomes apparent in the last half hour of License to Wed. That’s when the film begins to slow down and become more serious, especially when Ben skulks around Reverend Frank’s house in hopes of uncovering what he thinks are uncom- fortable secrets about the pastor’s personal life. But it’s a momentary awkwardness. Things rev up to speed again soon enough with a funny, if not too surprising, ending.

mjanuson@projo.com