diff --git a/Gemfile b/Gemfile
index 90353c7..aae9cad 100644
--- a/Gemfile
+++ b/Gemfile
@@ -5,17 +5,17 @@ source "https://rubygems.org"
 gemspec
 
 gem "capybara",            "3.40.0"
+gem "mutex_m",             "0.2.0"
 gem "puma",                "6.4.3"
 gem "pusher",              "2.0.3"
 gem "rake",                "13.2.1"
 gem "rspec",               "3.13.0"
-gem "rubocop",             "1.66.1"
+gem "rubocop",             "1.68.0"
 gem "rubocop-capybara",    "2.21.0"
 gem "rubocop-performance", "1.22.1"
 gem "rubocop-rake",        "0.6.0"
-gem "rubocop-rspec",       "3.0.5"
-gem "selenium-webdriver",  "4.25.0"
-gem "sinatra",             "3.2.0"
+gem "rubocop-rspec",       "3.2.0"
+gem "selenium-webdriver",  "4.26.0"
 gem "yard",                "0.9.37"
 
 group :test do
diff --git a/spec/support/application.rb b/spec/support/application.rb
index c1d0e6a..ad47da7 100644
--- a/spec/support/application.rb
+++ b/spec/support/application.rb
@@ -1,35 +1,61 @@
 # frozen_string_literal: true
 
-require "sinatra"
-require "tilt/erb"
-
-module Sinatra
-  class Application
-    set(:root,  proc { File.join(File.dirname(__FILE__), "application") })
-    set(:views, proc { File.join(root, "views") })
-
-    disable :logging
-
-    get "/" do
-      erb :index
-    end
-
-    post "/pusher/auth" do
-      channel  = Pusher[params[:channel_name]]
-      response = channel.authenticate(params[:socket_id], channel_data)
-
-      MultiJson.dump(response)
-    end
-
-    protected
-
-    def channel_data
-      return unless /^presence-/.match?(params[:channel_name])
-
-      {
-        user_id:   params[:socket_id],
-        user_info: { name: "Alan Turing" }
-      }
+require "rack"
+
+module PusherFake
+  module Testing
+    class Application
+      def call(env)
+        request = Rack::Request.new(env)
+
+        case request.path
+        when "/"
+          index
+        when "/pusher/auth"
+          authenticate(request.params)
+        when %r{\A/javascripts}
+          asset(request.path)
+        else
+          [404, {}, []]
+        end
+      end
+
+      private
+
+      def asset(path)
+        headers = { "content-type" => "text/javascript" }
+        root    = File.join(File.dirname(__FILE__), "application")
+        body    = File.read(File.join(root, "public", path))
+
+        [200, headers, [body]]
+      end
+
+      def authenticate(params)
+        channel  = Pusher[params["channel_name"]]
+        response = channel.authenticate(params["socket_id"], channel_data(params))
+        headers  = { "Content-Type" => "application/json" }
+
+        [200, headers, [MultiJson.dump(response)]]
+      end
+
+      def channel_data(params)
+        return unless /^presence-/.match?(params["channel_name"])
+
+        {
+          user_id:   params["socket_id"],
+          user_info: { name: "Alan Turing" }
+        }
+      end
+
+      def index
+        headers  = { "content-type" => "text/html" }
+        root     = File.join(File.dirname(__FILE__), "application")
+        template = File.read(File.join(root, "views", "index.erb"))
+        erb      = ERB.new(template)
+        body     = erb.result(binding)
+
+        [200, headers, [body]]
+      end
     end
   end
 end
diff --git a/spec/support/capybara.rb b/spec/support/capybara.rb
index f9e5a94..1f17f38 100644
--- a/spec/support/capybara.rb
+++ b/spec/support/capybara.rb
@@ -2,6 +2,6 @@
 
 require "capybara/rspec"
 
-Capybara.app = Sinatra::Application
+Capybara.app = PusherFake::Testing::Application.new
 Capybara.server = :puma, { Silent: true }
 Capybara.default_driver = :selenium_chrome_headless