class RSpec::Core::Configuration

def output_stream=(value)
  if @reporter && !value.equal?(@output_stream)
    warn "RSpec's reporter has already been initialized with " \
      "#{output_stream.inspect} as the output stream, so your change to "\
      "`output_stream` will be ignored. You should configure it earlier for " \
      "it to take effect. (Called from #{CallerFilter.first_non_rspec_line})"
  else
    @output_stream = value
  end
end