PyTest fails to discover tests with imports which print output

[AndrewLister-STFC]

Environment data

• VS Code version: 1.38.1
• Extension version (available under the Extensions sidebar): 2019.9.34911
• OS and version: Windows10 1803 (remote dev on Ubuntu 18.04.3)
• Python version (& distribution if applicable, e.g. Anaconda): 2.7.15
• Type of virtual environment used (N/A | venv | virtualenv | conda | ...): N/A
• Relevant/affected Python packages and their versions: N/A (editted as found a minimal working example)
• 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): Jedi

Expected behaviour

PyTest should detect all available tests provided they match the requirements on naming conventions.

Actual behaviour

PyTest returns the error:

Test Discovery failed: 
SyntaxError: Unexpected token F in JSON at position 0

This seems to be due to the discovery reading from stdout, as it picks up the first letter of a message that is printed from within a python import, and therefore cannot parse it as JSON.
I think this is only an issue with prints occuring from sources external to python.

Steps to reproduce:

1. Create a minimal working example as follows:
   2 directories: "some_module", "tests"

"some_module" directory: "__init__.py", "funcs.py", "run_me.bat"

"__init__.py" : empty
"funcs.py" :

import os
def do_thing():
    pass
os.system(os.path.join(os.path.dirname(__file__), 'run_me.bat'))

"run_me.bat" :

ECHO hello world

"tests" directory: "__init__.py", "test_imports.py"

"__init__.py" : empty
"test_imports.py" :

import sys, os
sys.path.append(os.path.join(__file__, os.pardir, os.pardir))
from unittest import TestCase
from some_module import funcs
class Tester(TestCase):
    def test_import(self):
        pass

2. Now go to python.settings and check that pytest is being used
3. Check that the test appears in the "TEST: PYTHON" panel

Logs

Output for Python in the Output panel (View→Output, change the drop-down the upper-right of the Output panel to Python)

Python

/usr/bin/python ~/.vscode-server/extensions/ms-python.python-2019.9.34911/pythonFiles/testing_tools/run_adapter.py discover pytest -- -s --cache-clear

Python Test Log

python /home/eel23943/.vscode-server/extensions/ms-python.python-2019.9.34911/pythonFiles/testing_tools/run_adapter.py discover pytest -- -s --cache-clear
Test Discovery failed: 
SyntaxError: Unexpected token F in JSON at position 0

Output from Console under the Developer Tools panel (toggle Developer Tools on under Help; turn on source maps to make any tracebacks be useful by running Enable source map support for extension debugging)

Error Python Extension: 2019-09-24 09:16:31: Failed to parse discovered Test [Error: FrameworkManager-[Notice] Welcome to Mantid 4.1.0FrameworkManager-[Notice] Please cite: http://dx.doi.org/10.1016/j.nima.2014.07.029 and this release: http://dx.doi.org/10.5286/Software/Mantid4.1DownloadInstrument-[Notice] All instrument definitions up to date[{"rootid": ".", "tests": [{"source":  ...

Note: The rest of this message looks to be the correct format, but its very long so I'm only posting the start.

[karrtikr]

Closing as dup of #6594

[AndrewLister-STFC]

Closing as dup of #6594

Sorry, I hadn't spotted that one

[karrtikr]

Not a problem, thanks for reporting!