after=True: the temporary dir will always be deleted at the end of the test.
after=False: the temporary dir will always be left intact at the end of the test.
In order to run the equivalent of rm -r safely, only subdirs of the project repository checkout are allowed if
an explicit tmp_dir is used, so that by mistake no /tmp or similar important part of the filesystem will
get nuked. i.e. please always pass paths that start with ./.
Each test can register multiple temporary directories and they all will get auto-removed, unless requested
otherwise.
Temporary sys.path override
If you need to temporary override sys.path to import from another test for example, you can use the
ExtendSysPath context manager. Example:
```python
import os
from transformers.testing_utils import ExtendSysPath
bindir = os.path.abspath(os.path.dirname(file))
