Connect trainer, lightning module and datamodule without calling .fit() or .test()

[nilsleh]

I have a lightning module that implements a sort of calibration computation during on_before_test_start() where I access a dataloader through the datamodule via self.trainer.datamodule.train_dataloader() , do some computation and use that in the predict_step().

Now I would like to use the predict_step() directly without having to call .test() and iterating over the entire dataloader. But if I don't do that, I get an RuntimeError: Lightningmodule is not attached to a Trainer. Therefore, I am wondering whether there is a way to "manually" do this part to avoid calling .test()?