Add some additional testing and comments surrounding the PaperTrail::Model::InstanceMethods#changed_notably? private method changes

lib/paper_trail/has_paper_trail.rb

@@ -366,6 +366,10 @@ module PaperTrail
         end
       end
 
+      # This method is invoked in order to determine whether it is appropriate to generate a new version instance.
+      # Because we are now using `after_(create/update/etc)` callbacks, we need to go out of our way to
+      # ensure that during updates timestamp attributes are not acknowledged as a notable changes
+      # to raise false positives when attributes are ignored.
       def changed_notably?
         if self.paper_trail_options[:ignore].any? && (changed & self.paper_trail_options[:ignore]).any?
           (notably_changed - timestamp_attributes_for_update_in_model.map(&:to_s)).any?

spec/models/gadget_spec.rb

@@ -18,4 +18,51 @@ describe Gadget do
       expect { gadget.update_attribute(:updated_at, Time.now) }.to change{gadget.versions.size}.by(1)
     end
   end
+
+  describe "Methods" do
+    describe "Instance", :versioning => true do
+      describe "private" do
+        describe :changed_notably? do
+          subject { Gadget.new(:created_at => Time.now) }
+
+          # apparently the private methods list in Ruby18 is different than in Ruby19+
+          if RUBY_VERSION.to_f >= 1.9
+            its(:private_methods) { should include(:changed_notably?) }
+          end
+
+          context "create events" do
+            it { subject.send(:changed_notably?).should == true }
+          end
+
+          context "update events" do
+            before { subject.save! }
+
+            context "without update timestamps" do
+              it "should only acknowledge non-ignored attrs" do
+                subject.name = 'Wrench'
+                subject.send(:changed_notably?).should == true
+              end
+
+              it "should not acknowledge ignored attrs and timestamps only" do
+                subject.brand = 'Acme'
+                subject.send(:changed_notably?).should == false
+              end
+            end
+
+            context "with update timestamps" do
+              it "should only acknowledge non-ignored attrs" do
+                subject.name, subject.updated_at = 'Wrench', Time.now
+                subject.send(:changed_notably?).should == true
+              end
+
+              it "should not acknowledge ignored attrs and timestamps only" do
+                subject.brand, subject.updated_at = 'Acme', Time.now
+                subject.send(:changed_notably?).should == false
+              end
+            end
+          end
+        end
+      end
+    end
+  end
 end