I would love a semi-automated way to generate a power-profile for ESP-Home. Find a smart room heater with 3 levels perhaps, and use home assistant to gather values at "Off", "1/3", "2/3", "3/3", with a downstream power plug as reference (and a known consumption of the downstream plug as well).
So I can just take my EspHome plug and very quickly generate a standard set of mapping values for voltage and wattage.
The easy way is with a resistive space heater and a multimeter. I keep a big, dumb, thrifted "oil-filled radiator" space heater around just to use as a big, safe 3-speed dummy load with reasonably OK repeatability (nichrome heaters do not have perfect temperature coefficients, but they're stable-enough that using them to measure temperature quickly begins to be a non-starter).
The level of integration you choose is entirely up to you. I don't do this kind of thing much, so I'm OK with kludging together a test rig as-needed with a handheld meter and tearing it apart when I'm done. This makes good use of my own time and tools, according to my personal proclivities.
But if I were doing it often, then I might buy the equivalent of the HOPI meter that Big Clive uses in many of his videos. It displays current and voltage, multiplies them to get power, and also displays power factor -- concurrently, on separate digital displays, in real time.
Or I might build something: A box with a current shunt with some panel-mount meters and appropriate connectors would not be too challenging to put together in an afternoon with parts from Amazon and Lowes, depending on one's ability and desire to deal with sheet metal at home. (I use galvanized steel handy boxes and cover plates from Lowes for all kinds of small-ish stuff. They're cheap, common, and durable-enough.)
Whatever the approach, a simple space heater with multiple literal-speeds seems like a cheap and useful way to make it happen unless you're trying to automate every part of it.
(But by then, making a dumb multi-speed space heater into a "smart" multi-speed space heater that can be activated programmatically with software like ESPHome and some relays is probably pretty much a no-brainer, isn't it?)
