Add test suite for flaubert tokenizer
This is tragic, the flaubert tokenizer has no tests. :crying_cat_face: 

Details to accompany this issue are coming soon, including a template to add these missing tests. This will probably be a good first issue.
This issue has been automatically marked as stale because it has not had recent activity. If you think this still needs to be addressed please comment on this thread.

Please note that issues that do not follow the [contributing guidelines](https://github.com/huggingface/transformers/blob/main/CONTRIBUTING.md) are likely to be ignored.<|||||>included into a more global issue: #16627