"ValueError: Pytest terminal summary report not found" when debugging pytester test that uses `runpytest_subprocess` on python 3.14

[DetachHead]

Type: Bug

Behaviour

when using pytest's pytester fixture to test my pytest plugin, my tests fail when debugging the test, but pass when running the tests normally. this only seems to occur on python 3.14. it works fine on python 3.13

tested with both pytest 8.4.0 and 9.0.0, same behavior.

Steps to reproduce:

1. create the following files:

# tests/test_foo.py

from pytest import Pytester

def test_foo(pytester: Pytester):
    pytester.makepyfile("def test_foo(): ...")
    result = pytester.runpytest_subprocess()
    result.assert_outcomes(passed=1)

# tests/conftest.py

pytest_plugins = ["pytester"]

// .vscode/settings.json
{
    "python.testing.pytestArgs": [
        "tests"
    ],
    "python.testing.unittestEnabled": false,
    "python.testing.pytestEnabled": true
}

2. click the test explorer and click the run button on test_foo (it passes)
3. right click the test and select "Debug Test" (it fails)

debug console output

python 3.14

Running pytest with args: ['-p', 'vscode_pytest', '--rootdir=/home/me/projects/test', '--capture=no', '/home/me/projects/test/tests/test_foo.py::test_foo']
============================= test session starts ==============================
platform linux -- Python 3.14.0, pytest-8.4.2, pluggy-1.6.0
rootdir: /home/me/projects/test
configfile: pyproject.toml
collected 1 item

tests/test_foo.py running: /home/me/projects/test/.venv/bin/python -mpytest --basetemp=/tmp/pytest-of-me/pytest-36/test_foo0/runpytest-0
     in: /tmp/pytest-of-me/pytest-36/test_foo0
0.00s - Debugger warning: It seems that frozen modules are being used, which may
0.00s - make the debugger miss breakpoints. Please pass -Xfrozen_modules=off
0.00s - to python to disable frozen modules.
0.00s - Note: Debugging will proceed. Set PYDEVD_DISABLE_FILE_VALIDATION=1 to disable this validation.
No module named pytest
F

=================================== FAILURES ===================================
___________________________________ test_foo ___________________________________

pytester = <Pytester PosixPath('/tmp/pytest-of-me/pytest-36/test_foo0')>

    def test_foo(pytester: Pytester):
        pytester.makepyfile("def test_addition(): ...")
        result = pytester.runpytest_subprocess()
>       result.assert_outcomes(passed=1)

/home/me/projects/test/tests/test_foo.py:6:
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
/home/me/projects/test/.venv/lib/python3.14/site-packages/_pytest/pytester.py:566: in parseoutcomes
    return self.parse_summary_nouns(self.outlines)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

cls = <class '_pytest.pytester.RunResult'>, lines = []

    @classmethod
    def parse_summary_nouns(cls, lines) -> dict[str, int]:
        """Extract the nouns from a pytest terminal summary line.

        It always returns the plural noun for consistency::

            ======= 1 failed, 1 passed, 1 warning, 1 error in 0.13s ====

        Will return ``{"failed": 1, "passed": 1, "warnings": 1, "errors": 1}``.
        """
        for line in reversed(lines):
            if rex_session_duration.search(line):
                outcomes = rex_outcome.findall(line)
                ret = {noun: int(count) for (count, noun) in outcomes}
                break
        else:
>           raise ValueError("Pytest terminal summary report not found")
E           ValueError: Pytest terminal summary report not found

/home/me/projects/test/.venv/lib/python3.14/site-packages/_pytest/pytester.py:584: ValueError
=========================== short test summary info ============================
FAILED tests/test_foo.py::test_foo - ValueError: Pytest terminal summary repo...
============================== 1 failed in 0.91s ===============================

python 3.13.8

Running pytest with args: ['-p', 'vscode_pytest', '--rootdir=/home/me/projects/test', '--capture=no', '/home/me/projects/test/tests/test_foo.py::test_foo']
============================= test session starts ==============================
platform linux -- Python 3.13.8, pytest-8.4.2, pluggy-1.6.0
rootdir: /home/me/projects/test
configfile: pyproject.toml
collected 1 item

tests/test_foo.py running: /home/me/projects/test/.venv/bin/python -mpytest --basetemp=/tmp/pytest-of-me/pytest-37/test_foo0/runpytest-0
     in: /tmp/pytest-of-me/pytest-37/test_foo0
============================= test session starts ==============================
platform linux -- Python 3.13.8, pytest-8.4.2, pluggy-1.6.0
0.00s - Debugger warning: It seems that frozen modules are being used, which may
0.00s - make the debugger miss breakpoints. Please pass -Xfrozen_modules=off
0.00s - to python to disable frozen modules.
0.00s - Note: Debugging will proceed. Set PYDEVD_DISABLE_FILE_VALIDATION=1 to disable this validation.

rootdir: /tmp/pytest-of-me/pytest-37/test_foo0
collected 1 item

test_foo.py .                                                            [100%]

============================== 1 passed in 0.01s ===============================
.

============================== 1 passed in 1.54s ===============================

note the "No module named pytest" that gets printed when running with python 3.14, that looks sus.

debug console output

Diagnostic data

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

2025-11-12 01:25:53.146 [info] arg: --rootdir already exists in args, not adding.
2025-11-12 01:25:53.147 [info] Attempting to use temp directory for test ids file, file name: test-ids-c7f03da52498b119f6b8.txt
2025-11-12 01:25:53.147 [info] Environment variables set for pytest execution: PYTHONPATH=/home/me/.vscode-oss/extensions/ms-python.python-2025.16.0-universal/python_files, TEST_RUN_PIPE=/run/user/1000/python-test-results-274bda5030eacd4c916c, RUN_TEST_IDS_PIPE=/run/user/1000/test-ids-c7f03da52498b119f6b8.txt
2025-11-12 01:25:53.147 [info] Running DEBUG pytest with arguments: --rootdir=/home/me/projects/test,--capture=no for workspace /home/me/projects/test 

2025-11-12 01:25:53.148 [info] Using configuration in workspace
2025-11-12 01:25:55.958 [info] Test Result named pipe /run/user/1000/python-test-results-274bda5030eacd4c916c  cancelled

Extension version: 2025.16.0
VSCodium version: VSCodium 1.105.17075 (14bd1561ce547502e6ff1968090dc18c49160aab, 2025-10-21T20:24:03.344Z)
OS version: Linux x64 6.8.0-87-generic
Modes:

• Python version (& distribution if applicable, e.g. Anaconda): 3.14.0
• Type of virtual environment used (e.g. conda, venv, virtualenv, etc.): Venv
• Value of the python.languageServer setting: None

[eleanorjboyd]

if you instead create a launch.json config and try running pytest that way does it work?

[DetachHead]

same thing seems to happen with the following launch.json:

{
  "version": "0.2.0",
  "configurations": [
    {
      "name": "pytest with args",
      "type": "debugpy",
      "request": "launch",
      "module": "pytest",
      "args": "${command:pickArgs}",
      "justMyCode": false
    }
  ]
}