class HfArgumentParserTest(unittest.TestCase):
    @mockenv(TRANSFORMERS_VERBOSITY="error")
    def test_env_override(self):
        env_level_str = os.getenv("TRANSFORMERS_VERBOSITY", None)
```
At times an external program needs to be called, which requires setting PYTHONPATH in os.environ to include
multiple local paths. A helper class transformers.test_utils.TestCasePlus comes to help:
```python
from transformers.testing_utils import TestCasePlus
class EnvExampleTest(TestCasePlus):
    def test_external_prog(self):
        env = self.get_env()
        # now call the external program, passing env to it
```
Depending on whether the test file was under the tests test suite or examples it'll correctly set up
env[PYTHONPATH] to include one of these two directories, and also the src directory to ensure the testing is
