What is the test for making a surety in a personal injury case?

In Bauer v. Bank of Montreal (1980), 1980 CanLII 12 (SCC), 110 D.L.R. (3d) 424 at p. 427, [1980] 2 S.C.R. 102, 10 B.L.R. 209, McIntyre J., who gave the judgment of the court, said: ... it is open to the parties to make their own arrangements, and a surety is competent to contract himself out of the protection of the equitable rule requiring preservation of his security.