What is the test for adding additional evidence in a defence?

Duff, J. in the case of MacDonald v. Pier, supra, at p. 384 says: “Upon that point the law is quite clear, but it does not follow that notice of the additional evidence must be given in the pleadings or that it is necessary that the pleadings should mention the evidence or refer to the evidence which the plaintiff intends to offer. It is not necessary, just as it is not necessary in a case in which corroboration is required by law of the plaintiff’s testimony.”