asserts replaced by exception for text classification task with test.
Haha it looks like you got the chance of being reviewed twice at the same time and got the same suggestion twice x)
Anyway it's all good now so we can merge ! Thanks for the feedback. 
I have replaced only a single assert in text_classification.py along with a unit test to verify an exception is raised based on https://github.com/huggingface/datasets/issues/3171 . 

I would like to first understand the code contribution workflow. So keeping the change to a single file rather than making too many changes. Once this gets approved, I will look into the rest. 

Thanks. 