Refactor running stage routing
No we can't in the current state of the codebase. Trainer.predict relies on self.trainertesting to be True for routing the code in the test part of the evaluation loop, and if we set self._running_stage = RuningStage.PREDICTING, it would route to validation and we won't gather the prediction.
I plan to properly refactor routing in a follow up PR as it is currently a big mess.
Originally posted by @tchaton in #5579 (comment)