fails:Hash#fetch returns the value for key
fails:Hash#fetch raises a KeyError if key is not found
fails:Hash#fetch returns default if key is not found when passed a default
fails:Hash#fetch returns value of block if key is not found when passed a block
fails:Hash#fetch gives precedence to the default block over the default argument when passed both
fails:Hash#fetch raises an ArgumentError when not passed one or two arguments
