Only track changed values when persisted state is Dirty

[#1355 state:resolved]

lib/dm-core/resource/state/dirty.rb

@@ -44,9 +44,9 @@ def track(subject, value)
             if original_attributes[subject].eql?(value)
               original_attributes.delete(subject)
             end
-          else
+          elsif !value.eql?(original = get(subject))
             # track the original value
-            original_attributes[subject] = get(subject)
+            original_attributes[subject] = original
           end
         end
 

spec/semipublic/resource/state/dirty_spec.rb

@@ -127,7 +127,7 @@ class ::Author
     supported_by :all do
       describe 'with attributes that keep the resource dirty' do
         before do
-          @key   = @model.properties[:name]
+          @key   = @model.properties[:id]
           @value = @key.get!(@resource)
         end
 
@@ -136,6 +136,8 @@ class ::Author
         it 'should return a Dirty state' do
           should equal(@state)
         end
+
+        its(:original_attributes) { should == { @model.properties[:name] => 'Dan Kubb' } }
       end
 
       describe 'with attributes that make the resource clean' do