Fix cacheable_attributes_spec.rb by adding column_names

spec/models/concerns/cacheable_attributes_spec.rb

@@ -20,6 +20,10 @@ describe CacheableAttributes do
         @_last ||= new('foo' => 'a', 'bar' => 'b')
       end
 
+      def self.column_names
+        %w[foo bar baz]
+      end
+
       attr_accessor :attributes
 
       def initialize(attrs = {}, *)
@@ -75,13 +79,13 @@ describe CacheableAttributes do
 
     context 'without any attributes given' do
       it 'intializes a new object with the defaults' do
-        expect(minimal_test_class.build_from_defaults.attributes).to eq(minimal_test_class.defaults)
+        expect(minimal_test_class.build_from_defaults.attributes).to eq(minimal_test_class.defaults.stringify_keys)
       end
     end
 
     context 'with attributes given' do
       it 'intializes a new object with the given attributes merged into the defaults' do
-        expect(minimal_test_class.build_from_defaults(foo: 'd').attributes[:foo]).to eq('d')
+        expect(minimal_test_class.build_from_defaults(foo: 'd').attributes['foo']).to eq('d')
       end
     end