ImportError: cannot import name 'test_external_redis' running

I try to run the following command in Ray’s official docker image, after cloning the Github repo:

pip install pytest
python -m pytest -v python/ray/tests/

It responded with:

ImportError while loading conftest ‘/home/ray/ray/python/ray/tests/’.
python/ray/tests/ in
from ray._private.test_utils import (
E ImportError: cannot import name ‘test_external_redis’ from ‘ray._private.test_utils’ (/home/ray/anaconda3/lib/python3.7/site-packages/ray/_private/

What did I miss? It’s just Step 1 from the Getting Started: Installing Ray — Ray 1.12.1