[MODEL] Port all integration tests to rspec (elastic#837)

Author: estolfo

elasticsearch-model/Rakefile

@@ -34,20 +34,17 @@ namespace :test do
 
   desc "Run unit tests against ActiveModel 3, 4 and 5"
   task :unit do
+  end
+
+  desc "Run integration tests against latest stable ActiveModel (5)"
+  task :integration do
     ['3.0.gemfile', '4.0.gemfile', '5.0.gemfile'].each do |gemfile|
       ['bundle exec rake test:run_unit', 'bundle exec rspec'].each do |cmd|
         sh "BUNDLE_GEMFILE='#{File.expand_path('../gemfiles/'+gemfile, __FILE__)}' #{cmd}"
       end
     end
   end
 
-  desc "Run integration tests against latest stable ActiveModel (5)"
-  task :integration do
-    #sh "BUNDLE_GEMFILE='#{File.expand_path('../gemfiles/3.0.gemfile', __FILE__)}' bundle exec rake test:run_integration"
-    #sh "BUNDLE_GEMFILE='#{File.expand_path('../gemfiles/4.0.gemfile', __FILE__)}' bundle exec rake test:run_integration"
-    sh "BUNDLE_GEMFILE='#{File.expand_path('../gemfiles/5.0.gemfile', __FILE__)}' bundle exec rake test:run_integration"
-  end
-
   desc "Run unit and integration tests"
   task :all do
     Rake::Task['test:unit'].invoke

elasticsearch-model/gemfiles/4.0.gemfile

@@ -10,6 +10,7 @@ gemspec path: '../'
 gem 'activemodel',  '~> 4'
 gem 'activerecord', '~> 4'
 gem 'sqlite3' unless defined?(JRUBY_VERSION)
+gem 'mongoid', '~> 5'
 
 group :development, :testing do
   gem 'rspec'