Testing of a Li* cell management system, what is the best approach?

[PeterFW]

Hello! 
For the past months i have been building a small open source handheld LED light.

I want to test the circuit as thoroughly as i can before i put the final schematics online for others to build their own.

But i ran into a small problem, i can simulate a bunch of conditions and failures but i have a hard time testing the battery circuit properly. 
I need a Voltage source that can sink current to simulate battery charging, i can get around that to an extend with my bench power supply but i can not sink current with that. 

The next best tool i could find, that would do that, is a source measure unit but after i had a look what they cost, that is out the window.

I lack suitable search terms to ask google for it, all i can come up with does not lead me were i want to go.

If that is not enough information, here is my project page for the light, that is all the information i have: 
https://hackaday.io/project/21001-brightenmacher

Thank you!