When exit handlers that print to standard out are registered using the atexit module, pytest test discovery fails.

Environment data

• VS Code version: 1.36.1
• Extension version (available under the Extensions sidebar): 2019.6.24221
• OS and version: Ubuntu Linux 18.04.2
• Python version (& distribution if applicable, e.g. Anaconda): Python 3.7.4
• Type of virtual environment used (N/A | venv | virtualenv | conda | ...): virtualenv
• Relevant/affected Python packages and their versions: pytest
• 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

I would expect the relevant tests to be discovered.

Actual behaviour

Test discovery fails because extra text is appended to whatever output is used to store the JSON description of the discovered tests, which subsequently causes a SyntaxError when parsing.

Steps to reproduce:

Allow test discovery to run on the minimal demonstration repository here: https://github.com/joel-wright/pytest-discovery-atexit

Logs

Output for Python Test Log:

python /home/jjw/.vscode/extensions/ms-python.python-2019.6.24221/pythonFiles/testing_tools/run_adapter.py discover pytest -- -s --cache-clear
Test Discovery failed: 
SyntaxError: Unexpected token I in JSON at position 436