Testing should include pouring in a similar manner to the way bartenders pour on the job. If they pour with both hands, they should be tested with both hands. If they pour 1 ¼ ounces with the right hand while pouring ½ ounce with the other hand at the same time, they should be tested in a similar manner. Set up 2 glasses or mixing tins and pour those amounts simultaneously and see how they do. If a bartender picks up two bottles in one hands to pour equal amounts from both, say ½ ounces each, have them do it and see if the total poured comes out to 1 ounce. If your bar has a specialty drink recipe that is popular, design a test that reflects the portions and procedures used with that drink (2 handed, multiple bottle, etc.)
In the download section of this site is a sample test sheet for overall portion testing. Modify it to fit your bar recipes portions. Keep in mind that the smaller portions offer the largest percentage over-pour probabilities so do not over emphasize your standard shot size while ignoring the smaller ones.
A note about pouring high viscosity liquors like Kaluha or Baileys Irish Cream. Liquors that contain a large percentage of sugar will pour much slower than the basic vodka, gin, scotch, etc. The same is true if you keep, say a vodka, in a freezer. In order to keep the timing close to your regular liquors you might use a larger opening pour spout on those kinds of liquors. It will take some experimenting to determine the time it takes to pour a shot with the higher viscosity brands. For example, I always used a pour spout that took 1 ¼ seconds to pour a shot size of 1 ¼ ounces. In such a case you could find a wider opening pour spout that closely matches the 1 ¼ second time to pour the higher viscosity brand for the same size shot. Another thing I have done with a high viscosity, high cost brand that was not poured on a regular basis was to put a jigger next to that bottle on the back bar and have bartenders use it when that brand was called for. (Be sure to test the accuracy of any jigger with the EXACTO-POUR™™ tube before using it.)