In the past when thermostats and sensors were much less reliable I used to hang them in a pot of water on the stove and slowly heat it up while monitoring them, and also the water temperature with a cooking thermometer. (Both are hanging high in the water and NOT resting on the bottom of the pot.)
I still do this, but recently they have all been spot on, and it is only force of habit, and the worry about fake parts, making me still do it.
In the 1960s, 70s and 80s we used to find about one in three of the waxstat types was off temp and about one in ten never worked at all, this for Jag, Ford, BL, and Vauxhall. Some stats had a tickler to let past air and a tiny flow of water and this had to be at the top when installed as a guarantee the bulb was always in the water.
Sensors were usually much more reliable. The gauge ones either worked or were open circuit. But the switch type as used on the Kenlowe electric fans we all added tended to be less reliable, and a standard mod was to use instead a linear sensor and potentiometer and a couple of transistors to drive a relay.