add integration test

test/integration/app.rb

@@ -0,0 +1,6 @@
+require 'sinatra'
+
+get '/app_file' do
+  content_type :txt
+  settings.app_file
+end

test/integration_test.rb

@@ -0,0 +1,22 @@
+require File.expand_path('../helper', __FILE__)
+require 'rbconfig'
+require 'open-uri'
+
+class IntegrationTest < Test::Unit::TestCase
+  it 'starts a top level application' do
+    cmd = []
+    app_file = File.expand_path('../integration/app.rb', __FILE__)
+    if RbConfig.respond_to? :ruby
+      cmd << RbConfig.ruby.inspect
+    else
+      file, dir = RbConfig::CONFIG.values_at('ruby_install_name', 'bindir')
+      cmd << File.expand_path(file, dir).inspect
+    end
+    cmd << "-I" << File.expand_path('../../lib', __FILE__).inspect
+    cmd << app_file.inspect
+    cmd << "2>&1"
+    pipe = IO.popen(cmd.join(" "))
+    assert_equal open('http://localhost:4567/app_file').read, app_file
+    Process.kill("TERM", pipe.pid)
+  end
+end