I am building a device that can power other devices (it has a voltage regulator, battery controller, etc...).

What is a good way to measure how much current it will provide, and/or test if it will provide a specific maximum current?

Normally, my device will be asked to provide 100-200 mA, but, I would like it to be able to provide 1000 mA max.

I can try to power another device like an Arduino (50-100 mA) or a 1000 mA motor I have, but I am thinking there should be a better way.

That wouldn't test intermediate levels like 200 mA or 500 mA. Plus the 1000 mA motor produces feedback which could be bad.