Add failing test for AMS::Model accessor vs. attributes mutation

test/active_model_serializers/model_test.rb

@@ -4,7 +4,7 @@ module ActiveModelSerializers
   class ModelTest < ActiveSupport::TestCase
     include ActiveModel::Serializer::Lint::Tests
 
-    def setup
+    setup do
       @resource = ActiveModelSerializers::Model.new
     end
 
@@ -18,5 +18,52 @@ module ActiveModelSerializers
 
       assert_equal model_instance.read_attribute_for_serialization(:key), value
     end
+
+    def test_attributes_can_be_read_for_serialization
+      klass = Class.new(ActiveModelSerializers::Model) do
+        attributes :one, :two, :three
+      end
+      original_attributes = { one: 1, two: 2, three: 3 }
+      instance = klass.new(original_attributes)
+
+      # Initial value
+      expected_attributes = { id: nil, one: 1, two: 2, three: 3 }.with_indifferent_access
+      assert_equal expected_attributes, instance.attributes
+      assert_equal 1, instance.one
+      assert_equal 1, instance.read_attribute_for_serialization(:one)
+
+      # Change via accessor
+      instance.one = :not_one
+
+      expected_attributes = { id: nil, one: :not_one, two: 2, three: 3 }.with_indifferent_access
+      assert_equal expected_attributes, instance.attributes
+      assert_equal :not_one, instance.one
+      assert_equal :not_one, instance.read_attribute_for_serialization(:one)
+    end
+
+    def test_id_attribute_can_be_read_for_serialization
+      klass = Class.new(ActiveModelSerializers::Model) do
+        attributes :id, :one, :two, :three
+      end
+      self.class.const_set(:SomeTestModel, klass)
+      original_attributes = { id: :ego, one: 1, two: 2, three: 3 }
+      instance = klass.new(original_attributes)
+
+      # Initial value
+      expected_attributes = { id: :ego, one: 1, two: 2, three: 3 }.with_indifferent_access
+      assert_equal expected_attributes, instance.attributes
+      assert_equal 1, instance.one
+      assert_equal 1, instance.read_attribute_for_serialization(:one)
+
+      # Change via accessor
+      instance.id = :superego
+
+      expected_attributes = { id: :superego, one: 1, two: 2, three: 3 }.with_indifferent_access
+      assert_equal expected_attributes, instance.attributes
+      assert_equal :superego, instance.id
+      assert_equal :superego, instance.read_attribute_for_serialization(:id)
+    ensure
+      self.class.send(:remove_const, :SomeTestModel)
+    end
   end
 end