add test for after_rollback

lib/paper_trail/has_paper_trail.rb

@@ -181,6 +181,8 @@ module PaperTrail
         (source_version || send(self.class.versions_association_name).last).try(:whodunnit)
       end
 
+      # Invoked after rollbacks to ensure versions records are not created
+      # for changes that never actually took place
       def clear_rolled_back_versions
         send(self.class.versions_association_name).reload
       end

spec/models/widget_spec.rb

@@ -85,6 +85,26 @@ describe Widget, :type => :model do
         expect(widget.version).to eq(widget.versions.last)
       end
     end
+
+    describe :after_rollback do
+      let(:rolled_back_name) { 'Big Moo' }
+
+      before do
+        widget.transaction do
+          widget.update_attributes!(name: rolled_back_name)
+          widget.update_attributes!(name: described_class::EXCLUDED_NAME)
+        end
+      rescue ActiveRecord::RecordInvalid
+        widget.name = nil
+        widget.save
+      end
+
+      it 'does not create an event for changes that did not happen' do
+        widget.versions.map(&:changeset).each do |changeset|
+          expect(changeset.fetch('name', [])).to_not include(rolled_back_name)
+        end
+      end
+    end
   end
 
   describe "Association", :versioning => true do

test/dummy/app/models/widget.rb

@@ -2,6 +2,10 @@ class Widget < ActiveRecord::Base
   has_paper_trail
   has_one :wotsit
 
+  EXCLUDED_NAME = 'Biglet'
+
+  validates :name, exclusion: { in: [EXCLUDED_NAME] }
+
   if ::ActiveRecord::VERSION::MAJOR >= 4 # `has_many` syntax for specifying order uses a lambda in Rails 4
     has_many :fluxors, lambda { order(:name) }
   else