gistfile1.diff

diff --git a/spec/unit/mongoid/dirty_spec.rb b/spec/unit/mongoid/dirty_spec.rb
index e412abc..43103c9 100644
--- a/spec/unit/mongoid/dirty_spec.rb
+++ b/spec/unit/mongoid/dirty_spec.rb
@@ -45,6 +45,18 @@ describe Mongoid::Dirty do
       end
     end
 
+    context "when the attribute is mutated in place" do
+      before do
+        @person = Person.new(:title => "Grand Poobah")
+        @person.title.sub!("Grand", "Most High")
+      end
+
+      it "tracks field changes" do
+        @person.attribute_change("title").should ==
+          [ "Grand Poobah", "Most High Poobah" ]
+      end
+    end
+
     context "when the attribute is removed" do
 
       before do