During practice of anything a person fails many times, that's why it's called practice.
You don't need to test to it then do you? It's already built in and acknowledged by the understanding of what practice is.
Ah, I see! It seems we're simply thinking of different things when we say 'testing'. I was thinking of the many tiny moments that happen all the time in practice, when we repeatedly try an exercise or technique many times, sometimes successfully and sometimes not... I'm also thinking of situations where I, for example, deliberately make _myself_ fail in a specific task in some exercise or technique, as a little experiment to see what works or doesn't.