Visual Studio Code – VSCode cannot locate packages in unit tests

I’ve got a project with a suite of Python unit tests (using the unittest framework) that import Pytorch and cv2.
I am able to run them all from the command line with

python -m unittest discover -s tests/

But get import errors in the VSCode UI when I try to load them:

Failed to import test module: test_overlays
Traceback (most recent call last):
  File "XXXAppDataLocalContinuumanaconda3libunittestloader.py", line 436, in _find_test_path
    module = self._get_module_from_name(name)
  File "XXXAppDataLocalContinuumanaconda3libunittestloader.py", line 377, in _get_module_from_name
    __import__(name)
  File "XXXteststest_overlays.py", line 13, in <module>
...
    import torch
ModuleNotFoundError: No module named 'torch'

My project is structured as a "wrapper application" importing utilities from a core library:

main_proj/
   library/
      packages and modules importing torch
   tests/
      unit tests for the application

The tests generally test only the wrapper application (there are separate tests for the library), but I occasionally import modules from library/.

Because the tests are outside main_proj/library, I need to add the library explicitly to the path at the top of each unit test:

import unittest
import sys
import os, os.path

sys.path.append(os.path.join(os.getcwd(), 'library'))

Why does this arrangement work just fine from the command line, but not from VSCode?