error in azure

[sangyx]

When I run the pytest in the azure pipelines, there are some errors:

2020-07-16T17:11:42.4458845Z =========================== short test summary info ============================
2020-07-16T17:11:42.4459936Z ERROR notebooks/linear regression.ipynb::Cell 0 - _queue.Empty
2020-07-16T17:11:42.4461052Z ERROR notebooks/linear regression.ipynb::Cell 1 - _queue.Empty
2020-07-16T17:11:42.4462191Z ERROR notebooks/linear regression.ipynb::Cell 2 - _queue.Empty
2020-07-16T17:11:42.4463308Z ERROR notebooks/linear regression.ipynb::Cell 3 - _queue.Empty
2020-07-16T17:11:42.4464443Z ERROR notebooks/quickstart.ipynb::Cell 0 - _queue.Empty
2020-07-16T17:11:42.4466990Z ERROR notebooks/quickstart.ipynb::Cell 1 - _queue.Empty
2020-07-16T17:11:42.4468282Z ERROR notebooks/quickstart.ipynb::Cell 2 - _queue.Empty

While the code is correct on my computer. Could you help me? My code is in:
https://github.com/sangyx/udiff/tree/master/notebooks
The full log is in:
https://dev.azure.com/Quansight-Labs/ec065212-e5ec-49f2-a977-57e90302356b/_apis/build/builds/699/logs/18