What is the test for exclusion of a party while another party is giving evidence?

Then he said this at p. 511: The cases are well reviewed in Pam v. Gale [1950] 2 WWR 802 (Man.) and I need not go through them. I do not think they establish that a party has a legal right to be present at all times. The weight of authority holds, I think, that either at a trial or on discovery a party cannot be excluded while his co-party testifies, without cause shown. But I do not think the onus of showing cause thus put on the opposite party is a heavy one; and I think the onus is lighter on discovery than at a trial, since the possibility of injustice from exclusion is more remote. Even at a trial, I think the chance of injustice being done in this way is extremely small. But in many cases the chances of injustice to the opposite party from refusal to exclude may be very substantial. I think the benefit of any real doubt should be given to the party asking for exclusion. If from the pleadings or otherwise it appears that the examinations of the co-parties will cover the same ground, and that their credibility will be a factor, then it seems to me their exclusion should be ordered.