Error in setUpTestData() with --parallel test execution causes abort with unclear exception and stack trace

[Glenn Matthews]

Given the following toy test example:

from django.test import TestCase


class AbortingTest(TestCase):
    @classmethod
    def setUpTestData(cls):
        raise RuntimeError("Boo!")

    def test_pass(self):
        pass


class AnotherAbortingTest(TestCase):
    @classmethod
    def setUpTestData(cls):
        raise RuntimeError("Boo Too!")

    def test_pass(self):
        pass

the errors are reported clearly when running tests in sequence (without --parallel):

EE
======================================================================
ERROR: setUpClass (tests.test_error.AbortingTest)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/usr/local/lib/python3.12/site-packages/django/test/testcases.py", line 1466, in setUpClass
    cls.setUpTestData()
  File "tests/test_error.py", line 7, in setUpTestData
    raise RuntimeError("Boo!")
RuntimeError: Boo!

======================================================================
ERROR: setUpClass (tests.test_error.AnotherAbortingTest)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/usr/local/lib/python3.12/site-packages/django/test/testcases.py", line 1466, in setUpClass
    cls.setUpTestData()
  File "tests/test_error.py", line 16, in setUpTestData
    raise RuntimeError("Boo Too!")
RuntimeError: Boo Too!

----------------------------------------------------------------------

However, when tests are run with --parallel, test execution instead aborts with a very unclear stack trace that doesn't even include any of the test code in question:

Destroying test database for alias 'default'...
Destroying test database for alias 'default'...
Emptying test database "default"...
Database default emptied!
Preserving test database for alias 'default'...
Traceback (most recent call last):
  File "/usr/local/lib/python3.12/site-packages/django/core/management/__init__.py", line 442, in execute_from_command_line
    utility.execute()
  File "/usr/local/lib/python3.12/site-packages/django/core/management/__init__.py", line 436, in execute
    self.fetch_command(subcommand).run_from_argv(self.argv)
  File "/usr/local/lib/python3.12/site-packages/django/core/management/commands/test.py", line 24, in run_from_argv
    super().run_from_argv(argv)
  File "/usr/local/lib/python3.12/site-packages/django/core/management/base.py", line 412, in run_from_argv
    self.execute(*args, **cmd_options)
  File "/usr/local/lib/python3.12/site-packages/django/core/management/base.py", line 458, in execute
    output = self.handle(*args, **options)
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.12/site-packages/django/core/management/commands/test.py", line 68, in handle
    failures = test_runner.run_tests(test_labels)
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.12/site-packages/django/test/runner.py", line 1061, in run_tests
    result = self.run_suite(suite)
             ^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.12/site-packages/django/test/runner.py", line 983, in run_suite
    return runner.run(suite)
           ^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.12/unittest/runner.py", line 240, in run
    test(result)
  File "/usr/local/lib/python3.12/unittest/suite.py", line 84, in __call__
    return self.run(*args, **kwds)
           ^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.12/site-packages/django/test/runner.py", line 549, in run
    handler(test, *args)
  File "/usr/local/lib/python3.12/unittest/runner.py", line 101, in addError
    super(TextTestResult, self).addError(test, err)
  File "/usr/local/lib/python3.12/unittest/result.py", line 17, in inner
    return method(self, *args, **kw)
           ^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.12/unittest/result.py", line 116, in addError
    self.errors.append((test, self._exc_info_to_string(err, test)))
                              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.12/unittest/result.py", line 195, in _exc_info_to_string
    output = sys.stdout.getvalue()
             ^^^^^^^^^^^^^^^^^^^
AttributeError: '_io.TextIOWrapper' object has no attribute 'getvalue'

[Sarah Boyce]

I couldn't replicate this on main with tblib installed (refs #25497)
If you have tblib installed, and are still getting an error on main, feel free to reopen with more details