What is the test for a jury in a professional negligence case?

[64] It has become standard practice in professional negligence cases for the jury to be asked to provide their reasons for any finding of negligence, in keeping with the observations of Sopinka J. in ter Neuzen v. Korn 1995 CanLII 72 (SCC), [1995] 3 S.C.R. 674 at para. 53: To avoid the problem encountered in this case due to the inscrutability of the jury's response to the question relating to negligence, and as a precaution to test the jury's understanding of the instruction, the question to the jury with respect to negligence should require that the jury specify in what respects the defendant was negligent. In a case in which the general rule applies, the answer will reveal whether the jury has understood and applied the judge's instruction that it must accept the standard practice as the legal standard against which the defendant's conduct must be measured. Additionally, in a case which falls within the exception to the general rule and where the jury can fix the standard irrespective of the expert evidence, the answer to the question will ensure that the standard which the jury has adopted is not unreasonable or unknown in law.