What harness do they use for testing?

Back in 2025 it was common to test models in a different harnesses.

I remember watching a guy on youtube, who was testing every new model in opencode, cline, codex, claude, etc.

Why did it come out of fashion ?

EDIT: ah, yeah. the point was that a harness would often affect results (task completion rate, I think) for more than 10%