Cannot run pytest-cov with ddtrace installed in the same project

[ddarricau]

Summary
Basically I am unable to run test coverage on a project that includes both ddtrace and pytest-cov

Expected vs actual result
I should be able to do so

Reproducer
In order to reproduce I have a very simple project with

[tool.poetry.dependencies]
python = "^3.12"
pytest = "^8.3.3"
pytest-cov = "^6.0.0"
ddtrace = "2.12.0"

And a test file

def test_ddtrace_coverage():
    assert 1 == 1

Whenever I run the command COVERAGE_FILE=foo COVERAGE_CORE=sysmon pytest --cov=. tests/test_ddtrace_coverage.py I get the following error

  File "/Users/didierdarricau/Library/Caches/pypoetry/virtualenvs/ddtrace-coverage-test-5TsU0QvL-py3.12/lib/python3.12/site-packages/coverage/sysmon.py", line 226, in start
    sys_monitoring.use_tool_id(self.myid, "coverage.py")
ValueError: tool 1 is already in use

Note that this only happens when using the COVERAGE_CORE=sysmon flag, it seems that both ddtrace and pytest-cov request the same tool_id in that module. Note that using this flag is important to me as it significantly shortens the CI run time at my job.

I am not sure who should resolve the issue so I am also posting an issue on the pytest-cov repo.

Also not that if I use a ddtrace version < 2.12.0 it works fine.

[romainkomorndatadog]

Thanks for the report, @ddarricau .

We're winning the race to sys_monitoring.use_tool_id() with our own call as a result of imports, but the main issue is that we shouldn't be calling use_tool_id() unless we're actually collecting coverage.

@vitor-de-araujo or I should refactor the code so that we only call use_tool_id() if instrument_all_lines() is actually called.

[ddarricau]

Great thank you !