fails:File.open opens the file when passed mode, num and permissions
fails:File.open opens the file when passed mode, num, permissions and block
fails:File.open raises an IOError when read in a block opened with File::RDONLY|File::APPEND mode
fails:File.open raises an IOError if the file exists when open with File::RDONLY|File::APPEND
fails:File.open opens directories
fails:File.open raises an ArgumentError if passed the wrong number of arguments
