Inegration context for RSpec

ActionDispatch::Testing::Integration requires smth else and
defines Rails, so had to change `defined?(Rails)` all over the code.

lib/telegram/bot/rspec/integration.rb

@@ -0,0 +1,49 @@
+RSpec.shared_context 'telegram/bot/integration' do
+  let(:bot) { Telegram.bot }
+  let(:from_id) { 123 }
+  let(:chat_id) { 456 }
+  let(:default_message_options) { {from: {id: from_id}, chat: {id: chat_id}} }
+  let(:controller_path) do
+    route_name = Telegram::Bot::RoutesHelper.route_name_for_bot(bot)
+    Rails.application.routes.url_helpers.public_send("#{route_name}_path")
+  end
+  let(:request_headers) do
+    {
+      'ACCEPT' => 'application/json',
+      'Content-Type' => 'application/json',
+    }
+  end
+  let(:clear_session?) { described_class.respond_to?(:session_store) }
+  before { described_class.session_store.clear if clear_session? }
+
+  include Telegram::Bot::RSpec::ClientMatchers
+
+  def dispatch(update)
+    if ActionPack::VERSION::MAJOR >= 5
+      post(controller_path, params: update.to_json, headers: request_headers)
+    else
+      post(controller_path, update.to_json, request_headers)
+    end
+  end
+
+  def dispatch_message(text, options = {})
+    dispatch message: default_message_options.merge(options).merge(text: text)
+  end
+
+  def dispatch_command(*args)
+    options = args.last.is_a?(Hash) ? args.pop : {}
+    dispatch_message("/#{args.join ' '}", options)
+  end
+
+  # Matcher to check response. Make sure to define `let(:chat_id)`.
+  def respond_with_message(expected)
+    raise 'Define chat_id to use respond_with_message' unless defined?(chat_id)
+    send_telegram_message(bot, expected, chat_id: chat_id)
+  end
+end
+
+RSpec.configure do |config|
+  if config.respond_to?(:include_context)
+    config.include_context 'telegram/bot/integration', :telegram_bot
+  end
+end