Impossible to only download a test split
I've spent a significant amount of time trying to locate the split object inside my _split_generators() custom function.
Then after diving [in the code](https://github.com/huggingface/datasets/blob/5ff3670c18ed34fa8ddfa70a9aa403ae6cc9ad54/src/datasets/load.py#L2558) I realized that `download_and_prepare` is executed before! split is passed to the dataset builder in `as_dataset`.

If I'm not missing something, this seems like bad design, for the following use case:

> Imagine there is a huge dataset that has an evaluation test set and you want to just download and run just to compare your method.

Is there a current workaround that can help me achieve the same result?

Thank you,