If you've gotten to know the company somewhat (several interviews that went well), give them a counteroffer:
"I know how important it is to test my skills before hiring me, so I'd like to propose an even more in-depth assessment: I'll work for you as a contractor for two weeks. If your team likes my work, you can hire me as an employee."
I don't know if it would work, but if you really can't spare the time to do assessments, it's worth a shot.