fails:File::Stat#file? returns true if the named file exists and is a regular file.
fails:File::Stat#file? accepts an object that has a #to_path method
fails:File::Stat#file? returns true if the null device exists and is a regular file.
fails:File::Stat#file? raises a TypeError if not passed a String type
windows:File::Stat#file? raises an ArgumentError if not passed one argument
