This idea was appeared in my head earlier but I thought that it was wrong. Many thank to Olga Gerasimenok for helping me to understand that it's not bad.
So, we propose that periodically (say - one time per 2-3 weeks) business analyst should quickly test the system and review whether the functionality is implemented correctly not from functional point of view but from "business requirements" side.
We think it's necessary because nor tester neither developers don't understand how it should be really implemented completely right. On development side only business analyst understand it right, on other side - only customer (and even not always) understand it. But rare customer will review the functionality so often and in full measure. So this duty rest on analysts' shoulders.
I've experimented with this one time. Analyst said - "it was really right solution to do this test! Good job!"
So, I think we will continue to apply this practice.