I have actually done that very test on my 64 GTO in college.
946 cubic centimeter fuel tank (1 quart of gas), (1/4th of a gallon of gas).
Disconnect the gas line from the fuel pump and plug it.
Hook up the 946 cubic centimeter tank to the fuel pump and start the run on a measured course (mapped out) on the country roads around the university. Run the course and see what your mileage was (assuming city type driving). Mileage was just that. How far did you travel. The load we put on the vehicle was a real world load. Normal 30 mph type speeds.
Emissions and F.E. Tests are basically the same deal. You run a US ftp 75-cvs cycle and read the emissions on two exhaust collection sample bags (a collection bag that is filled for 505 seconds and a second collection bag that is filled for the remainder of the 1372 second emissions cycle. A hot start bag is filled for 505 seconds at the end of the testing.
see link.
https://www.dieselnet.com/standards/cycles/ftp75.php
Tom V.
ps HIS, you would have to have a pretty accurate "higher value" gram scale to read the weight of your container and the fuel used in the test.