> This is true for a company sponsored Green Card application, not H-1B visa.
IIRC, that's typically gamed. It's been awhile, but I knew a couple of guys who went through that and I recall they postings "to find an American citizen" were written hyper-specifically in order avoid hiring anyone, and if anyone actually applied, I'd imagine the interview would have been tough with a predetermined outcome.
It's a crappy system. Tests like that should be at the start, not at the end. If they're at the end, it just wastes everyone's time and subverts the test: even if you think the company should hire more Americans, are you going to undermine your coworker in such a way that they may get deported? Is it fair to do that after someone's put down roots? (No.)