Install ONNX
Making: https://github.com/onnx/onnx

conda install -c conda-forge protobuf numpy
sudo apt-get install protobuf-compiler libprotoc-dev
pip install onnx
pip install pytest==2.8 nbval

I started with PIP Install Pytest NBval and reported the following error,

Then I pass the prompt nbVAL 0.9.6 requires Pytest> =2.8, but you’ll have pytest 0.0.0 which is incompatible. I made a version of PyTest and retyped the command to install it successfully.
Then I input Pytest to verify whether the installation is successful. The prompt says that I did not install it. According to the following prompt, I input the following command and then input Pytest.

sudo apt install python-logilab-common

For example, If I go into a project folder and type PyTest, the output looks like the following to indicate that the installation is successful.