What is the test for obtaining leave to cross-examine a witness?

In the decision of Regina v. Garofoli, (1990), 1990 CanLII 52 (SCC), 60 C.C.C. (3d) 161, [1990] 2 S.C.R. 1421, 80 C.R. (3d) 317, Sopinka J. related the pre-conditions for cross- examination on the affidavit for an authorization such as this at page 198: “With respect to prolixity, I am in favour of placing reasonable limitations on the cross-examination. Leave must be obtained to cross-examine. The granting of leave must be left to the exercise of the discretion of the trial judge. Leave should be granted when the trial judge is satisfied that cross-examination is necessary to enable the accused to make full answer and defence. A basis must be shown by the accused for the view that the cross-examination will elicit testimony tending to discredit the existence of one of the pre-conditions to the authorization, as for example the existence of reasonable and probable grounds. When permitted, the cross-examination should be limited by the trial judge to questions that are directed to establish that there was no basis upon which the authorization could have been granted. The discretion of the trial judge should not be interfered with on appeal except in cases in which it has not been judicially exercised. While leave to cross-examine is not the general rule, it is justified in these circumstances in order to prevent an abuse of what is essentially a ruling on the admissibility of evidence.”