Using sys settrace with pytest in python

Question

I want to trace the functions called and their return values for a test in python. I am using pytest module to call the test and sys.settrace for tracing the functions. However, this doesn't work and no functions are traced when I use pytest. It works when I use a locally defined function.

filename="../tests/models/reading_comprehension/naqanet_test.py::NumericallyAugmentedQaNetTest::test_model_can_train_save_and_load"
sys.settrace(trace_calls_and_returns)
sys.gettrace()
pytest.cmdline.main(filename.split(" "))

This is what I get:

============================= test session starts ==============================
platform linux -- Python 3.6.8, pytest-5.3.1, py-1.8.0, pluggy-0.13.1
plugins: flaky-3.6.1, cov-2.8.1
collected 1 item

.../tests/models/reading_comprehension/naqanet_test.py .            [100%]

============================== 1 passed in 5.43s ===============================

Is there a way to use trace with pytest? Or some other way to handle it? I would like to handle this programmatically.

=============EDIT 1 ===============

Minimum reproducible example:

mytest.py

from unittest import TestCase


class MyTest(TestCase):
    def testMe(self):
        a=5
        b=6
        k=self.m(5,6)

    def m(self, a, b):
        return max(a,b)

tracetest.py

import sys
import pytest


def trace_calls(frame, event, arg):
    if event != 'call':
        return
    co = frame.f_code
    func_name = co.co_name
    caller = frame.f_back
    caller_line_no = caller.f_lineno if caller is not None else None
    caller_filename = caller.f_code.co_filename if caller is not None else None
    print('Call to %s on line %s of %s from line %s of %s' % \
        (func_name, func_line_no, func_filename,
         caller_line_no, caller_filename))
    return


sys.settrace(trace_calls)

pytest.main(["mytest.py"])

The output does not have the function "m" in "mytest.py"

=================== EDIT 2 ===================

Found the solution:

Just need to add this option to pytest:

pytest.main(["--capture=no", "mytest.py"])

Thats it! :)

I got the hint from here