What is the test for fair use of a copyrighted work?

The fair use doctrine "permits and requires courts to avoid rigid application of the copyright statute when, on occasion, it would stifle the very creativity which that law is designed to foster." Campbell v. Acuff-Rose Music, Inc., 510 U.S. 569, 577, 114 S.Ct. 1164, 127 L.Ed.2d 500 (1994) (internal quotation marks omitted). Consequently, 17 U.S.C. 107 establishes that fair use of a copyrighted work is not an infringement of copyright and lays out four factors to apply when considering whether the use of a work is "fair":