ImportError: cannot import name 'test_external_redis' running test_mini.py

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/test_mini.py

It responded with:

ImportError while loading conftest ‘/home/ray/ray/python/ray/tests/conftest.py’.
python/ray/tests/conftest.py:29: 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/test_utils.py)

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