Question: What is the title of this mockumentary film that Fred Willard, Christopher Guest, and Rob Reiner were involved with?

Context paragraphs:
Christopher Guest: Christopher Haden-Guest, 5th Baron Haden-Guest (born February 5, 1948), simply known as Christopher Guest, is an English-American screenwriter, composer, musician, director, actor, and comedian who holds dual British and American citizenship.  Guest is most widely known in Hollywood for having written, directed and starred in his series of comedy films shot in mock-documentary (mockumentary) style.  Many scenes and character backgrounds in Guest's films are written and directed, although actors have no rehearsal time and the ensemble improvise scenes while filming them.  The series of films began with "This Is Spinal Tap" (directed by Rob Reiner), and continued with "Waiting for Guffman", "Best In Show", "A Mighty Wind", "For Your Consideration", and "Mascots".

Spinal Tap (band): Spinal Tap (stylized as Spın̈al Tap, with a dotless letter "i" and a metal umlaut over the "n") is a parody band spoofing the style of rock heavy metal groups.  The band first appeared on a 1979 ABC TV sketch comedy pilot called "The T.V. Show", starring Rob Reiner.  The sketch, actually a mock promotional video for the song "Rock and Roll Nightmare", was written by Reiner and the band, and included songwriter/performer Loudon Wainwright III on keyboards.  Later the band became the fictional subject of the 1984 rockumentary/mockumentary film "This Is Spinal Tap".  The band members are portrayed by Michael McKean (as David St. Hubbins), Christopher Guest (as Nigel Tufnel) and Harry Shearer (as Derek Smalls).

Fred Willard: Frederick Charles "Fred" Willard (born September 18, 1939) is an American actor, comedian, voice actor and writer, best known for his improvisational comedy.  He is known for his roles in the Rob Reiner mockumentary film "This Is Spinal Tap", the Christopher Guest mockumentary films "Waiting for Guffman", "Best in Show", "A Mighty Wind", "For Your Consideration", and "Mascots", and the "" films.  He is an alumnus of The Second City.  He received three Emmy nominations for his recurring role on the TV series "Everybody Loves Raymond" as Robert Barone's father-in-law, Hank MacDougall.  In 2010 he received an Emmy nomination for Outstanding Guest Actor in a Comedy Series for his role on the ABC TV series "Modern Family" as Phil Dunphy's father, Frank Dunphy.

Mascots (2016 film): Mascots is a 2016 mockumentary from Christopher Guest that premiered on Netflix on October 13, 2016, featuring Guest, Jane Lynch, Parker Posey, Fred Willard, Ed Begley, Jr., Christopher Moynihan, Don Lake, Zach Woods, Chris O'Dowd, Bob Balaban, and Jennifer Coolidge.

Waiting for Guffman: Waiting for Guffman is a 1997 American mockumentary comedy film co-written and directed by Christopher Guest.  The film's cast includes Catherine O'Hara, Eugene Levy, Fred Willard, and Parker Posey.

The Princess Bride (film): The Princess Bride is a 1987 American romantic fantasy adventure comedy-drama film directed and co-produced by Rob Reiner, and starring Cary Elwes, Robin Wright, Mandy Patinkin, Chris Sarandon, Wallace Shawn, André the Giant and Christopher Guest.  Adapted by William Goldman from his 1973 novel of the same name, it tells the story of a farmhand named Westley, accompanied by befriended companions along the way, who must rescue his true love Princess Buttercup from the odious Prince Humperdinck.  The story is presented in the film as a book being read by a grandfather (Peter Falk) to his sick grandson (Fred Savage), thus effectively preserving the novel's narrative style.

This Is Spinal Tap: This Is Spinal Tap (stylized as This Is Spın̈al Tap) is a 1984 American rock music mockumentary comedy film directed, co-written, scored by, and starring Rob Reiner, and co-starring Christopher Guest, Michael McKean and Harry Shearer.  The film portrays the fictional British heavy metal band Spinal Tap.  The film satirizes the wild personal behavior and musical pretensions of hard rock and heavy metal bands, as well as the hagiographic tendencies of rock documentaries of the time.  The three main members of Spinal Tap—David St. Hubbins, Derek Smalls and Nigel Tufnel—are played by actors McKean, Shearer, and Guest, respectively.  The three actors play their musical instruments and speak with mock English accents throughout the movie.  Reiner appears as Marty Di Bergi, the maker of the documentary.  Other actors in the movie are Tony Hendra as group manager Ian Faith, and June Chadwick as St. Hubbins' interfering girlfriend Jeanine.  Actors Paul Shaffer, Fred Willard, Fran Drescher, Bruno Kirby, Howard Hesseman, Ed Begley, Jr., Patrick Macnee, Anjelica Huston, Vicki Blue, Dana Carvey, Billy Crystal and Linnea Quigley all play supporting roles or make cameo appearances in the movie.

G-Sale: G-Sale is a 2003 mockumentary film about garage sales and the people who are obsessed by them.  The film is reminiscent of the movies of Christopher Guest and won several film festival awards.

The Magic of Belle Isle: The Magic of Belle Isle is a 2012 drama film directed by Rob Reiner and written by Guy Thomas.  The film stars Morgan Freeman, Virginia Madsen, Emma Fuhrmann, Madeline Carroll, Kenan Thompson, Nicolette Pierini, Kevin Pollak and Fred Willard.  The film was released on July 6, 2012, by Magnolia Pictures.  In the UK the film was entitled 'Once More'.

Stu Osborn Show: The Stu Osborn Show is a 2007 web viral video advertisement for Microsoft.  It is made to look like a mockumentary of a fictional television interview show of the same name.  The video is directed by Christopher Guest who is well known for being the creative force behind other mockumentaries like "Waiting for Guffman" and "Best In Show".  It stars Michael Hitchcock as Stu Osborn, the awkward and somewhat disoriented "host" and Fred Willard as a failed businessman-turned-author who is Osborn's "guest."  Much of the dialogue is improvised by the actors.  Both Hitchcock and Willard are frequent performers in Guest's films.

Supporting paragraphs: Fred Willard Christopher Guest
Answer: This Is Spinal Tap