add support of mongoid collection serialization

test/serializer_support_test.rb

@@ -20,6 +20,11 @@ module ActiveRecord
   end
 end
 
+module Mongoid
+  class Criteria
+  end
+end
+
 class SerializerSupportTest < ActiveModel::TestCase
   test "it returns nil if no serializer exists" do
     assert_equal nil, RandomModel.new.active_model_serializer
@@ -37,5 +42,10 @@ class SerializerSupportTest < ActiveModel::TestCase
     ActiveSupport.run_load_hooks(:active_record)
     assert_equal ActiveModel::ArraySerializer, ActiveRecord::Relation.new.active_model_serializer
   end
+
+  test "it automatically includes array_serializer in mongoid/criteria" do
+    ActiveSupport.run_load_hooks(:mongoid)
+    assert_equal ActiveModel::ArraySerializer, Mongoid::Criteria.new.active_model_serializer
+  end
 end