Add a reproduction case for this issue :(

.rvmrc

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+rvm use ruby-1.8.7@async-sinatra-test-bug --create

Gemfile

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+source :gemcutter
+
+gem "rake"
+gem "async_sinatra"
+gem "rack-test"
+gem "cucumber"
+gem "rspec"

app/server.rb

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+
+require 'rubygems'
+require 'sinatra/async'
+
+class AsyncTest < Sinatra::Base
+  register Sinatra::Async
+
+  aget '/' do
+    body "hello"
+  end
+end

features/step_definitions/derp_steps.rb

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+Given /^I am a bug$/ do
+end
+
+When /^I get "([^"]*)"$/ do |arg1|
+  aget '/'
+  em_async_continue
+end
+
+Then /^I should asplode$/ do
+  last_response.body.should == "hello"
+end
+

features/support/env.rb

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+
+ENV["RACK_ENV"] = 'test'
+require 'rspec'
+require 'test/unit'
+require 'rack/test'
+require "sinatra/async/test"
+
+require File.expand_path(File.dirname(__FILE__) + "/../../app/server")
+
+module AppRunner
+  def app
+    AsyncTest.new
+  end
+end
+World(Test::Unit::Assertions, Sinatra::Async::Test::Methods, AppRunner)
+
+def post_json(path,json)
+  header 'Content-Type', 'application/json'
+  apost path, json.to_json
+  em_async_continue
+  last_response
+end
+

features/test.feature

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+Feature: Herp
+
+  Scenario: Derp
+    Given I am a bug
+    When I get "/"
+    Then I should asplode