gistfile1.rb

require 'spec_helper'

describe TCPSocket do
  describe '#write_nonblock' do
    let(:payload) { 'JUNK IN THE TUBES' }

    it "writes if the operation won't block" do
      setup_tcp do |client, peer|
        client.write_nonblock(payload).should eq payload.length
        peer.read(payload.length).should eq payload
      end
    end
    
    it "raises Errno::EWOULDBLOCK if the operation would block" do
      setup_tcp do |client, peer|
        expect do
          loop { client.write_nonblock(payload) }
        end.to raise_exception(Errno::EWOULDBLOCK)
      end
    end

    def setup_tcp(&block)
      addr, tcp_port = '127.0.0.1', 12321

      server = TCPServer.new(addr, tcp_port)
      client = TCPSocket.new(addr, tcp_port)
      peer   = server.accept

      block.call(client, peer)
      
      client.close
      server.close
      peer.close
    end
  end
end

Oh, that's beautiful.

@dkubb thanks!