__del__ method incorrectly reported as missing in a problem with circular references

[andymwood]

Summary

The following problem has two objects that reference each other and a __del__ method in one of the classes. pytest-cov incorrectly reports that the __del__ method hasn't been called.

Expected vs actual result

Expected 100% coverage. Get 91% coverage.

Reproducer

$ python3.10 -m venv venv
$ . venv/bin/activate
$ pip install pytest-cov
$ pytest --cov=. --cov-report=term-missing test_module.py 
================================================================== test session starts ===================================================================
platform linux -- Python 3.10.11, pytest-7.4.0, pluggy-1.2.0
rootdir: ...
plugins: cov-4.1.0
collected 1 item                                                                                                                                         

test_module.py .                                                                                                                                   [100%]
A.__del__


---------- coverage: platform linux, python 3.10.11-final-0 ----------
Name             Stmts   Miss  Cover   Missing
----------------------------------------------
test_module.py      10      1    90%   3
----------------------------------------------
TOTAL               10      1    90%


=================================================================== 1 passed in 0.06s ====================================================================

Versions

$ pip list
Package        Version
-------------- -------
coverage       7.2.7
exceptiongroup 1.1.2
iniconfig      2.0.0
packaging      23.1
pip            23.0.1
pluggy         1.2.0
pytest         7.4.0
pytest-cov     4.1.0
setuptools     65.5.0
tomli          2.0.1
$ python --version
Python 3.10.11

Code

test_module.py:

class A:
    def __del__(self):
        print('\nA.__del__')


class B:
    pass


def test_case():
    x = A()
    x.y = B()
    x.y.x = x
    assert x is not None