What is the test for a jury to ask a witness to their opinion on competence?

In Wright v. Tatham (1838) 5 Cl & F 670, at 690-1, 7 ER 559, at 566, appears the following: “ * * * but, competency in the main, is a question of fact, and the jury are to draw their conclusion from the evidence of the facts before them, not from the opinions which others may have formed from the facts not before the jury. I admit that, in practice, where the witness to facts is present, it is by no means uncommon to ask directly for his opinion; such a question it would be idle to object to; for, the objection would only lead to a detailed inquiry into particular facts, which the witness is there ready to go into. Nothing, therefore, would be gained by it. I am not, however, aware that this question has ever, upon argument, been decided to be correct in form.”