diff --git a/test/serializers/serializer_for_test.rb b/test/serializers/serializer_for_test.rb
index 413fe299..8dd9bd41 100644
--- a/test/serializers/serializer_for_test.rb
+++ b/test/serializers/serializer_for_test.rb
@@ -3,25 +3,44 @@ require 'test_helper'
 module ActiveModel
   class Serializer
     class SerializerForTest < Minitest::Test
-      def setup
-        @array = [1, 2, 3]
-        @previous_array_serializer = ActiveModel::Serializer.config.array_serializer
+      class ArraySerializerTest < Minitest::Test
+        def setup
+          @array = [1, 2, 3]
+          @previous_array_serializer = ActiveModel::Serializer.config.array_serializer
+        end
+
+        def teardown
+          ActiveModel::Serializer.config.array_serializer = @previous_array_serializer
+        end
+
+        def test_serializer_for_array
+          serializer = ActiveModel::Serializer.serializer_for(@array)
+          assert_equal ActiveModel::Serializer.config.array_serializer, serializer
+        end
+
+        def test_overwritten_serializer_for_array
+          new_array_serializer = Class.new
+          ActiveModel::Serializer.config.array_serializer = new_array_serializer
+          serializer = ActiveModel::Serializer.serializer_for(@array)
+          assert_equal new_array_serializer, serializer
+        end
       end
 
-      def teardown
-        ActiveModel::Serializer.config.array_serializer = @previous_array_serializer
-      end
+      class SerializerTest <  Minitest::Test
+        def setup
+          @profile = Profile.new
+          @model = ::Model.new
+        end
 
-      def test_serializer_for_array
-        serializer = ActiveModel::Serializer.serializer_for(@array)
-        assert_equal ActiveModel::Serializer.config.array_serializer, serializer
-      end
+        def test_serializer_for_existing_serializer
+          serializer = ActiveModel::Serializer.serializer_for(@profile)
+          assert_equal ProfileSerializer, serializer
+        end
 
-      def test_overwritten_serializer_for_array
-        new_array_serializer = Class.new
-        ActiveModel::Serializer.config.array_serializer = new_array_serializer
-        serializer = ActiveModel::Serializer.serializer_for(@array)
-        assert_equal new_array_serializer, serializer
+        def test_serializer_for_not_existing_serializer
+          serializer = ActiveModel::Serializer.serializer_for(@model)
+          assert_equal nil, serializer
+        end
       end
     end
   end