Add to .vscode/settings.json:

"python.testing.unittestArgs": [],
"python.testing.unittestEnabled": true,

In root of your project create a .env file:

MANAGE_PY_PATH=manage.py

if you don't want create .env file in root, add to .vscode/settings.json:

"python.envFile": "${workspaceFolder}/-your-folder-/.env"