fails:File.file? returns true if the named file exists and is a regular file.
fails:File.file? accepts an object that has a #to_path method
fails:File.file? returns true if the null device exists and is a regular file.
fails:File.file? raises an ArgumentError if not passed one argument
fails:File.file? raises a TypeError if not passed a String type
fails:FileTest.file? needs to be reviewed for spec completeness
