Test Discovery (unittest) failing in Insiders Extension

[astrowonk]

Issue Type: Bug

Unittest discovery in the new unit test API in the insiders extension appears to fail to properly find tests, when the old test discovery works fine.

Extension version: 2021.9.1106798209-dev
VS Code version: Code 1.59.0 (379476f0e13988d90fab105c5c19e7abc8b1dea8, 2021-08-04T23:11:51.081Z)
OS version: Darwin arm64 20.6.0
Restricted Mode: No

System Info

Item	Value
CPUs	Apple M1 (8 x 24)
GPU Status	2d_canvas: enabled gpu_compositing: enabled metal: disabled_off multiple_raster_threads: enabled_on oop_rasterization: enabled opengl: enabled_on rasterization: enabled skia_renderer: disabled_off_ok video_decode: enabled webgl: enabled webgl2: enabled
Load (avg)	2, 1, 2
Memory (System)	16.00GB (0.12GB free)
Process Argv	--crash-reporter-id 68686b81-af00-4876-bfbb-a517c41c7bb9
Screen Reader	no
VM	0%

A/B Experiments

vsliv368:30146709
vsreu685:30147344
python383cf:30185419
vspyt653:30270858
pythonvspyt602:30300191
vspor879:30202332
vspor708:30202333
vspor363:30204092
pythonvspyt639:30300192
pythontb:30283811
pythonvspyt551cf:30345471
pythonptprofiler:30281270
vshan820:30294714
vstes263:30335439
pythondataviewer:30285071
pythonvsuse255:30340121
vscod805:30301674
pythonvspyt200:30340761
vscextlang:30333561
binariesv615:30325510
pythonvssor306:30344512
bridge0708:30335490
vstre464:30346472
bridge0723:30346310

Sorry, I thought I'd be able to edit this in github before it just automatically created the issue. Editing to add details and screenshots. Unit tests in subfolders don't appear to be found at all in Insiders. I have created a simple example repo.

On released version (no Insiders python extension):

With Python Insiders Weekly (same behavior with daily):

Discovery works fine on the command line:

Structure is like in the example repo, one top level folder in the work space with different modules / tests in subfolders.

[karthiknadig]

@astrowonk Thanks for the repo. This should be fixed with #16906