Pinch test - basically can be done at any speed but usually done at WOT or idle.

Run engine to desired speed. Carefully reach in, beware of prop, and pinch off fuel line where it enters the carb.
If engine accelerates noticeably briefly then dies - too rich.
If engine just dies w/o increasing - too lean.
If engine accelerates just barely detectably - OK.
Test usually done first at WOT and then idle, adjust appropriate needle. Engine should accelerate smoothly from idle to WOT w/o stumbling.

Usually need to stop engine to safely adjust idle mixture.