How cold it keeps the food and how often, if ever, the food spoils.

why?

Purchase an appliance thermometer and test the refrigerator. Below is how you would test your appliance after a power outage. You can also use it to test efficiency. Using Appliance Thermometers Refrigerator/Freezer Thermometers Refrigerator/freezer thermometers are specially designed to provide accuracy at cold temperatures. For safety, it is important to verify the temperature of refrigerators and freezers. Refrigerators should maintain a temperature no higher than 40°F. Frozen food will hold its top quality for the longest possible time when the freezer maintains 0°F. Most refrigerators and freezers can be easily adjusted to run colder or warmer. The temperature control is usually accessible in the refrigerator part of the appliance. Check the owner’s manual for specific details on adjusting the temperature. An adjustment period is often required when changing the temperature. To measure the temperature in the refrigerator: Put the thermometer in a glass of water and place in the middle of the refrigerator. Wait 5 to 8 hours. If the temperature is not 38 to 40°F, adjust the refrigerator temperature control. Check again after 5 to 8 hours. To measure the temperature in the freezer: Place the thermometer between frozen food packages. Wait 5 to 8 hours. If the temperature is not 0 to 2°F, adjust the freezer temperature control. Check again after 5 to 8 hours. An appliance thermometer can be kept in the refrigerator and freezer to monitor the temperature at all times. This can be critical in the event of a power outage. When the power goes back on, if the refrigerator is still 40°F and the freezer is 0°F or below, the food is safe. http://www.fsis.usda.gov/FactSheets/Appliance_Thermometers/index.asp

New refrigerators come with an "Energy" sticker on them.

The only way I know to do this is to connect a recording wattage meter ("watt meter" or "watt-hour meter" or "electricity usage monitor") between the fridge and the socket. It will tell you how many watts are used over a period of time. Ideally you should record wattage use over a whole year since, for a fridge, temperature of the room has a big effect on how much electricity the fridge uses. In any case, even using the meter for a day will give you SOME idea of how much electricity the fridge uses on a daily basis. {{ https://www.amazon.com/appliance-power-meter/s?k=appliance+power+meter }}

Carnot (maximum theoretical) Efficiency = Temperature inside / (Temperature outside - Temperature inside) If you want the overall efficiency at cooling, you probably want to calculate the theoretical coefficient of performance (as above) and then measure the actual coefficient of performance (by measuring the work input into the refrigerator and the heat output) and take the ratio of the two.

get your hands on a kilowatt hour meter and measure how much electricity its consuming.

We don't need refrigerators anymore. We have Biden and the Democrats. Thus, no groceries.