Avoid duplicate group membership emails

app/observers/users_group_observer.rb

@@ -4,6 +4,6 @@ class UsersGroupObserver < BaseObserver
   end
 
   def after_update(membership)
-    notification.update_group_member(membership)
+    notification.update_group_member(membership) if membership.group_access_changed?
   end
 end

spec/observers/users_group_observer_spec.rb

@@ -23,5 +23,10 @@ describe UsersGroupObserver do
       subject.should_receive(:notification)
       @membership.update_attribute(:group_access, UsersGroup::MASTER)
     end
+
+    it "does not send an email when the access level has not changed" do
+      subject.should_not_receive(:notification)
+      @membership.update_attribute(:group_access, UsersGroup::OWNER)
+    end
   end
 end