hey lukebyrne, Here it is some bash script that I have used to create a sample data set from a regular dataset. You can get inspired in order to build your own. You just need to shuffle and move some samples from train folder into valid folder. 20% of your examples should be in validation folder. The other folders are created/updated by fast.ai fw.
The test folder is usually used for kaggle competitions. This folder contains samples with no labels - on which you run your model, you get the predictions and you post them on the kaggle in order to get a feedback.