Testing the use of form_for to clone an existing record

I wanted to be able to clone fields from one record into a new record, so I added a select box to allow the user to select the record from which (s)he wanted to clone (using AJAX to dynamically update the view when (s)he selects such a record). In my #new action, I check to see if the :clone_from parameter points to a valid record and if it does, I set my @record parameter to that record (created via old_record.clone). If it doesn't point to a valid record, I set @record to Record.new.

Here's my problem...

in my view, I have

form_for record do |f| ... end

which generates a RESTful call to my #create action when @record was empty (i.e. filled in from Record.new), but generates a RESTful call to my #update action when @record is a clone of the old record.

Ahhhh.... this is why this mailing list is so helpful.... I start to write the email, I get to the part where I write "is a clone of the old record", and I think to myself, "Wait a minute! Did I really call #clone when I went down that path?".... checked the code... found out that I didn't... called #clone... problem solved.

Gee, thanks folks!!! You're the greatest!!! (especially those of you who kept reading this far :-))

OK, now I've updated the subject line to reflect my (new) real question... When I first discovered this behavior, I thought to myself, "I should write a test case that demonstrates this bug, fix the bug, and show that the test case now passes".

When I tried to write the functional test that demonstrated this (issue a #get call to the :new action with the :clone_from parameter set, issue a #post :create call with the modified clone), the test worked perfectly. I had to look at the logs or HTML source to see that I was calling #update instead of #create.

How could I have tested this? Is it even worth writing a test case to demonstrate the incorrect operation of code that simply had a typo in it?

What do you think?