Set up a row of 10+ hoppers fed from a chest. Put a lot of items into the chest, and wait until all of the hoppers should be transporting items. Lock all of the hoppers simultaneously, and run down the line of hoppers looking at the inventory of each one.

I expected that there would be a single item in each hopper in the chain, but one of them will be empty.

A simple setup would be to attach a comparator to the last hopper in the chain that then locks the entire chain upon it receiving an item.