I will add this, then, since you deleted your original posting of this.
It depends on what you’re looking to test. Generally, any test that you want to be representative of a situation for a certain device, needs to approximate said situation.
If you’re just testing whether or not a specific ESC can sustain X amount of amps, then generally you would use FOC open loop into a motor that can handle that current, and then monitor thermals.
Since that generally still leaves the battery in current relatively low, you could then set up a dynamometer to simlate torque load on a motor at a certain RPM, and funnel that back to require more current draw from the battery.
A power supply likely isn’t going to be able to provide 50-75v at tens of amps, unless you’ve got quite the budget. So a battery of a representative size would be appropriate.
Generally, most folks who are interested in testing such things simply use the most practical test jig available, which is an actual eskate they’ve built, and then substitute the part in to test.
Of course, that’s dangerous should the part fail, but it’s usually cheaper for someone who doesn’t have a whole shop’s worth of stuff to make testing jigs.
You could also design a specific PCB based testing jigs like what Future Motion does, but that takes engineering talent and money.
Adendum: DIY builders with enough reading, collaboration, and expertise in the parts they employ, generally have a reliable starting point for almost any application, since all of these parts and systems are based around the same philosphies of design.
Those who choose to push beyond those conventions do so at their own risk, as is the nature of testing things in any sense. @Takachi14 has an affinity for pushing insane amounts of current everywhere under his feet, and @Heathlewis I imagine has some expertise when it comes to testing the real world limits of the sheer RPM thresholds for his parts.
Every build is a test jig for something.
The best data comes from the community, as each member tries something and gives their data.
The best thing that I have ever found in helping to grow knowledge and expertise, is to actually read what the community says, and actually listen to it. Just a general thought.