What is the test for determining whether a plaintiff would have suffered a secondary injury if they had not suffered the primary injury?

… the question is whether the worker would have suffered the secondary injury but for — i.e. in the absence of — the primary injury. If the answer is yes, meaning the secondary injury would have happened anyway, then there is no causation and the secondary injury is not claim-related. But if the answer is no, the primary injury played a necessary role in bringing about the secondary injury, which is thus claim‑related. It should be noted that the primary injury does not need to be sole or most important cause of the secondary injury; as long as the former materially contributed to the latter, then causation is established: see Ison, above; Athey v. Leonati, 1996 CanLII 183 (SCC), [1996] 3 SCR 458 at para. 17. [emphasis added] [paragraph 36 of decision 20198853]