If you want to do this at the order level, there isn’t really a way to do this at the delivery point like there is for the receiving process.  You would end up having to create some other indicator that the testing work needs to be done.  Some ideas I can think of are:

• Add a non-inventory sales part to the Customer Order to indicate it is required
• Add an inventory sales part connected to a shop order if you need to record time for this testing
• Add a routing to the existing catalog numbers being used to do the testing so it appears during the build

There may be other possibilities depending on whether this is always test for this catalog number, always test for this customer, or only test when requested by a customer.  Those are all variables that I see would mean one works better than the other, but they would all be a process you would have to create around the proper signal, nothing I can think of out of the box.