pytest discovery seems to fail in Python 3.8

[albireox]

Environment data

• VS Code version: 1.4.10-insiders
• Extension version (available under the Extensions sidebar): 2019.12.51221-dev
• OS and version: macOS 10.15.1
• Python version (& distribution if applicable, e.g. Anaconda): 3.8.0
• Type of virtual environment used (N/A | venv | virtualenv | conda | ...): pyenv
• Relevant/affected Python packages and their versions: pytest 5.3.1
• Jedi or Language Server? (i.e. what is "python.jediEnabled" set to; more info How to update the language server to the latest stable version #3977): Language Server

Expected behaviour

Discovery tests works fine.

Actual behaviour

Discovery tests fails with error

SyntaxError: Unexpected token � in JSON at position 0"

Steps to reproduce:

I think this occurs only in Python 3.8 (the same code, in Python 3.7 works fine). The cause may be because in Python 3.8 pytests returns a the imp module is deprecated in favour of importlib; see the module's documentation for alternative uses warning. Not sure if that may be crashing the parsing of the output.

[brettcannon]

Thanks for the bug report! We just wanted to quickly acknowledge we received it and we will triage this as soon as we can.

[ericsnowcurrently]

@albireox, in the "Python" output panel you should see the command that the extension is running to discover tests. What is that command? What happens when you run it directly in the terminal?

[albireox]

I think the command being executed is

~/.pyenv/versions/jaeger9/bin/python ~/.vscode-insiders/extensions/ms-python.python-2019.11.50794/pythonFiles/testing_tools/run_adapter.py discover pytest -- --rootdir ~/Documents/Code/sdssv/jaeger -s --cache-clear tests

and the output in the terminal I get is

[ERROR]: Traceback (most recent call last):
  File "/Users/albireo/.vscode-insiders/extensions/ms-python.python-2019.11.50794/pythonFiles/testing_tools/run_adapter.py", line 18, in <module>
    main(tool, cmd, subargs, toolargs)
  File "/Users/albireo/.vscode-insiders/extensions/ms-python.python-2019.11.50794/pythonFiles/testing_tools/adapter/__main__.py", line 90, in main
    parents, result = run(toolargs, **subargs)
  File "/Users/albireo/.vscode-insiders/extensions/ms-python.python-2019.11.50794/pythonFiles/testing_tools/adapter/pytest/_discovery.py", line 35, in discover
    raise Exception('pytest discovery failed (exit code {})'.format(ec))
Exception: pytest discovery failed (exit code 4)

[ericsnowcurrently]

Thanks for the update. That output should have been preceded by the actual output of pytest itself. Please try running pytest directly:

~/.pyenv/versions/jaeger9/bin/python -m pytest --rootdir ~/Documents/Code/sdssv/jaeger -s --cache-clear tests

[albireox]

If I run that command I get

ERROR: usage: pytest.py [options] [file_or_dir] [file_or_dir] [...]
pytest.py: error: unrecognized arguments: --cov --cov-report html tests
  inifile: /Users/albireo/Documents/Code/sdssv/jaeger/pytest.ini
  rootdir: /Users/albireo/Documents/Code/sdssv/jaeger

This seems to be because I have in my pytest.init the line addopts = --cov jaeger --cov-report html -W ignore. If I remove it I get

~/.pyenv/versions/jaeger9/bin/python -m pytest --rootdir ~/Documents/Code/sdssv/jaeger -s --cache-clear tests
============================================================= test session starts =============================================================
platform darwin -- Python 3.8.0, pytest-5.3.1, py-1.8.0, pluggy-0.13.1
rootdir: /Users/albireo/Documents/Code/sdssv/jaeger, inifile: pytest.ini
collected 31 items                                                                                                                            

tests/test_bootloader.py ss
tests/test_fps.py sssssss
tests/test_positioner.py ssss
tests/test_trajectory.py s
tests/test_utils.py .................

============================================================== warnings summary ===============================================================
/Users/albireo/.pyenv/versions/3.8.0/envs/jaeger9/lib/python3.8/site-packages/_pytest/mark/structures.py:323
  /Users/albireo/.pyenv/versions/3.8.0/envs/jaeger9/lib/python3.8/site-packages/_pytest/mark/structures.py:323: PytestUnknownMarkWarning: Unknown pytest.mark.asyncio - is this a typo?  You can register custom marks to avoid this warning - for details, see https://docs.pytest.org/en/latest/mark.html
    warnings.warn(

tests/test_bootloader.py::test_bootloader
tests/test_bootloader.py::test_load_firmware
tests/test_fps.py::test_vfps
tests/test_fps.py::test_get_id
tests/test_fps.py::test_initialise
tests/test_fps.py::test_pollers
tests/test_fps.py::test_stop_pollers
tests/test_fps.py::test_pollers_delay
tests/test_fps.py::test_shutdown
tests/test_positioner.py::test_get_position
tests/test_positioner.py::test_goto
tests/test_positioner.py::test_goto_no_move
tests/test_positioner.py::test_goto_relative
tests/test_trajectory.py::test_send_trajectory
  /Users/albireo/.pyenv/versions/3.8.0/envs/jaeger9/lib/python3.8/site-packages/_pytest/python.py:156: PytestUnhandledCoroutineWarning: async def functions are not natively supported and have been skipped.
  You need to install a suitable plugin for your async framework, for example:
    - pytest-asyncio
    - pytest-trio
    - pytest-tornasync
    warnings.warn(PytestUnhandledCoroutineWarning(msg.format(pyfuncitem.nodeid)))

-- Docs: https://docs.pytest.org/en/latest/warnings.html
================================================ 17 passed, 14 skipped, 15 warnings in 14.27s =================================================

[ericsnowcurrently]

That makes sense. If pytest can't run then the extension can't do discovery. Is there anything we need to do to help with this?

[albireox]

I guess no. It seems installing the missing pytest extensions does fix it. Thanks!

[ericsnowcurrently]

Glad to help!