class FakeFS::File::Stat

def writable?
  # a file is writable if, and only if, it has the following bits:
  #   2 ( write permission )
  #   3 ( write + execute permission )
  #   6 ( read + write permission )
  #   7 ( read + write + execute permission )
  # for each group we will isolate the wanted numbers ( for owner, world, or group )
  # and see if the second bit is set ( as that is the bit for write )
  write_bit = 2
  check_if_bit_set(write_bit)
end