First pass at integration testing with ChildProcess

This adds one very basic test, which exercises the full RbReadline
stack. The test process is spawned and interacted with in a platform
agnostic way using ChildProcess[1].

1 - https://github.com/jarib/childprocess.git

test/bin/basic-readline

+require 'readline'
+
+loop do
+  line = Readline::readline(ARGV.first)
+  break if line.nil? || line == 'quit'
+  puts "You typed: #{line}"
+end

test/test_simple_io.rb

+require "test/unit"
+require "childprocess"
+require "tempfile"
+require "readline"
+
+module RbReadline
+  class << self
+    attr_accessor :_rl_term_mm, :term_has_meta
+  end
+end
+
+module ChildProcessHelperMethods
+  # If the terminal has a meta key, seek past the shell code that enables it.
+  def seek_past_meta
+    @stdout.rewind
+    RbReadline._rl_init_terminal_io ENV["TERM"]
+    if RbReadline.term_has_meta
+      @stdout.seek(RbReadline._rl_term_mm.size)
+    end
+  end
+
+  # Enter some text at the terminal.
+  def input(text)
+    pos = @stdout.pos
+    @stdin << text
+    sleep 0.2
+    @stdout.seek(pos)
+  end
+
+  # Setup and run the child process.
+  def setup_child_process(prompt)
+    @process = ChildProcess.build("ruby", "#{File.dirname(__FILE__)}/bin/basic-readline", prompt)
+    @process.duplex = true
+
+    @stdout = Tempfile.new("readline-stdout")
+    @stderr = Tempfile.new("readline-stderr")
+    @process.io.stdout = @stdout
+    @process.io.stderr = @stderr
+    @process.start
+    sleep 0.2
+    @stdin = @process.io.stdin
+    seek_past_meta
+  end
+end
+
+# A simple first pass at some integration testing.
+class TestSimpleIO < Test::Unit::TestCase
+  include ChildProcessHelperMethods
+
+  def teardown
+    @process.stop
+  end
+
+  def test_sending_input_and_reading_output
+    setup_child_process "> "
+
+    assert_equal @stdout.read, "> "
+    input "123\n"
+    assert_equal @stdout.readline.chomp, "You typed: 123"
+  end
+end