Make basic DSL for testing via tmux

Still not testing anything meaningful, but you can see the beginnings of
something useful and easy-enough-to-use here.

If the `#wait_for` fails, an exception is thrown and the session is left
running for debugging purposes.

test.rb

@@ -1,15 +1,61 @@
 #!/usr/bin/env ruby
 
-%x{tmux new-session -d -s ferret-test}
-%x{tmux send-keys -t ferret-test 'vim -u NONE' Enter}
-%x{tmux send-keys -t ferret-test ':set nocompatible' Enter}
-%x{tmux send-keys -t ferret-test ':set rtp+=#{Dir.pwd}' Enter}
-%x{tmux send-keys -t ferret-test ':runtime! plugin/ferret.vim' Enter}
-
-%x{tmux send-keys -t ferret-test \\\\ a usr/bin/env\\\\ Space ruby Enter}
-
-sleep 1
-%x{tmux capture-pane -t ferret-test}
-buffer = %x{tmux show-buffer}
-%x{tmux delete-buffer}
-puts buffer
+require 'shellwords'
+
+module DSL
+  module Constants
+    Backslash = '\\'
+    Enter = 'Enter'
+    Space = 'Space'
+  end
+
+  class << self
+    def escape(string)
+      Shellwords.shellescape(string)
+    end
+  end
+
+  class Session
+    WAIT_TIMEOUT = 5
+
+    def initialize(name)
+      @name = name
+    end
+
+    def send_keys(*args)
+      escaped = args.map { |arg| DSL.escape(arg) }
+      %x{tmux send-keys -t #{@name} #{escaped.join(' ')}}
+    end
+
+    def wait_for(pattern)
+      buffer = nil
+      start = Time.now
+      while (Time.now - start < WAIT_TIMEOUT)
+        %x{tmux capture-pane -t #{@name}}
+        buffer = %x{tmux show-buffer}
+        %x{tmux delete-buffer}
+        return buffer if buffer =~ pattern
+        sleep 0.25
+      end
+      raise "Failed to find pattern `#{pattern.inspect}` in session `#{@name}`"
+    end
+  end
+
+  def session(name, &block)
+    escaped_name = DSL.escape(name)
+    %x{tmux new-session -d -s #{DSL.escape(escaped_name)}}
+    Session.new(escaped_name).instance_eval(&block)
+    %x{tmux kill-session -t #{escaped_name}}
+  end
+end
+self.extend(DSL)
+Object.instance_eval { include DSL::Constants }
+
+session('ferret-test') do |name|
+  send_keys('vim -u NONE', Enter)
+  send_keys(':set nocompatible', Enter)
+  send_keys(":set rtp+=#{DSL.escape(Dir.pwd)}", Enter)
+  send_keys(':runtime! plugin/ferret.vim', Enter)
+  send_keys(Backslash, 'a', 'usr/bin/env', Backslash, Space, 'ruby', Enter)
+  wait_for(/module DSL/)
+end