This document discusses fuzz testing techniques. It describes generating random data and inputs to test systems in unexpected ways. This allows discovering bugs like hangs, crashes, and performance issues. Examples mentioned include testing a math library by generating random expressions, testing a text messaging system by simulating many parallel messages, and testing a tree parsing algorithm with huge randomly generated directory trees. Fuzz testing uncovered bugs in areas like regular expressions, logging libraries causing bottlenecks, and parsing hangs.