Issue with coverage and pymp

[AdityaGupta030697]

Describe the bug Issue with coverage and pymp (https://github.com/classner/pymp)

• It is giving CoverageWarning: No data was collected. (no-data-collected)
• For other libraries like multiprocessing, it is working as expected.

To Reproduce

# sample.py
def div(a, b):
    if b == 0:
        raise ValueError("b == 0")
    return a//b

# test_sample.py
from sample import div
import unittest
from multiprocessing import Process
import pymp

class TestSample(unittest.TestCase):
    def test_div(self):
        a = 5
        b = 2
        # p = Process(target=div, args=(a, b ))
        # p.start()
        # p.join()
        with pymp.Parallel(2) as p:
            for i in p.range(1):
                div(a, b)

if __name__ == "__main__":
    unittest.main()

# .coveragerc
[run]
include = *sample*
parallel      = True
concurrency   = multiprocessing,thread

[report]
ignore_errors = True

[html]
# Title that will be displayed in coverage report
title         = Code Coverage Report

1. What version of Python are you using? 3.9.7

2. What version of coverage.py shows the problem? 6.2

3. What versions of what packages do you have installed? pymp-pypi 0.4.5

4. What commands did you run?

# Using pymp
shell> coverage run test_sample.py 
../python3.9/site-packages/coverage/control.py:768: CoverageWarning: No data was collected. (no-data-collected)
  self._warn("No data was collected.", slug="no-data-collected")
.
----------------------------------------------------------------------
Ran 1 test in 0.181s

OK
../python-3.9/std/lib64/python3.9/site-packages/coverage/control.py:768: CoverageWarning: No data was collected. (no-data-collected)

shell> coverage combine && coverage report
Name             Stmts   Miss  Cover
------------------------------------
sample.py            4      1    75%
test_sample.py      12      0   100%
------------------------------------
TOTAL               16      1    94%

# Using multiprocessing: no warnings
shell> coverage run test_sample.py 
.
----------------------------------------------------------------------
Ran 1 test in 0.181s

OK

shell> coverage combine && coverage report
Name             Stmts   Miss  Cover
------------------------------------
sample.py            4      1    75%
test_sample.py      12      0   100%
------------------------------------
TOTAL               16      1    94%

Expected behavior I was not expecting this warning to come up as data was collected.

PS: Also tried upgrading coverage and pymp to the latest version: didn't help. TIA for looking into this.

[nedbat]

Hi, sorry I let this sit so long. I see the warning you mean, but I also see that after coverage combine, the data is all present. I'm not sure why the warning is happening. Are you finding that data is actually missing, or is it a spurious warning?

[AdityaGupta030697]

Hi @nedbat! Apologies for the late reply. It is just a spurious warning as the coverage numbers seem to be correct. Thanks again for looking into this!