MaxLengthORMTests.test_custom_max_lengths test fails when run in isolation

[Matt McDonald]

Attempting to run tests from the max_lengths tests package results in the following failure:

$ ./tests/runtests.py max_lengths  --verbosity=2
Testing against Django installed in '/home/me/Development/django/django' with up to 12 processes
Importing application max_lengths
Skipping setup of unused database(s): default, other.
System check identified no issues (0 silenced).
..E
======================================================================
ERROR: test_custom_max_lengths (max_lengths.tests.MaxLengthORMTests)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/usr/lib/python3.6/unittest/case.py", line 59, in testPartExecutor
    yield
  File "/usr/lib/python3.6/unittest/case.py", line 605, in run
    testMethod()
  File "/home/me/mmcdonald/Development/django/tests/max_lengths/tests.py", line 38, in test_custom_max_lengths
    p = PersonWithCustomMaxLengths.objects.create(**new_args)
  File "/home/me/Development/django/django/db/models/manager.py", line 82, in manager_method
    return getattr(self.get_queryset(), name)(*args, **kwargs)
  File "/home/me/Development/django/django/db/models/query.py", line 421, in create
    obj.save(force_insert=True, using=self.db)
  File "/home/me/Development/django/django/db/models/base.py", line 741, in save
    force_update=force_update, update_fields=update_fields)
  File "/home/me/Development/django/django/db/models/base.py", line 779, in save_base
    force_update, using, update_fields,
  File "/home/me/Development/django/django/db/models/base.py", line 870, in _save_table
    result = self._do_insert(cls._base_manager, using, fields, update_pk, raw)
  File "/home/me/Development/django/django/db/models/base.py", line 908, in _do_insert
    using=using, raw=raw)
  File "/home/me/Development/django/django/db/models/manager.py", line 82, in manager_method
    return getattr(self.get_queryset(), name)(*args, **kwargs)
  File "/home/me/Development/django/django/db/models/query.py", line 1175, in _insert
    return query.get_compiler(using=using).execute_sql(return_id)
  File "/home/me/Development/django/django/db/models/sql/compiler.py", line 1316, in execute_sql
    cursor.execute(sql, params)
  File "/home/me/Development/django/django/db/backends/utils.py", line 67, in execute
    return self._execute_with_wrappers(sql, params, many=False, executor=self._execute)
  File "/home/me/Development/django/django/db/backends/utils.py", line 76, in _execute_with_wrappers
    return executor(sql, params, many, context)
  File "/home/me/Development/django/django/db/backends/utils.py", line 84, in _execute
    return self.cursor.execute(sql, params)
  File "/home/me/Development/django/django/db/utils.py", line 89, in __exit__
    raise dj_exc_value.with_traceback(traceback) from exc_value
  File "/home/me/Development/django/django/db/backends/utils.py", line 84, in _execute
    return self.cursor.execute(sql, params)
  File "/home/me/Development/django/django/db/backends/sqlite3/base.py", line 391, in execute
    return Database.Cursor.execute(self, query, params)
django.db.utils.OperationalError: no such table: max_lengths_personwithcustommaxlengths

----------------------------------------------------------------------
Ran 3 tests in 0.122s

FAILED (errors=1)

From a cursory glance, this appears to be a result of the max_lengths.tests.MaxLengthORMTests class inappropriately extending from unittest.TestCase when it should extend from django.test.TestCase, as the test_custom_max_lengths method relies upon database and table creation having been performed.

Interestingly, when executed as as part of a run of the full test suite, the failure does not seem to occur. My guess would be that the test case is being grouped into a suite with at least one other test case inheriting from django.test.TestCase, which implicitly provides the database initialization required by the max_lengths test instead of skipping the db setup when the test is run in isolation.

​https://github.com/django/django/blob/398afba084679f1055926f6f91bd33fe124a92c5/django/test/runner.py#L606

[Sage Abdullah]

​PR.

[Mariusz Felisiak <felisiak.mariusz@…>]

In 5a92bb0:

Fixed #30295 -- Fixed max_lengths.tests.MaxLengthORMTests when run in isolation.

[Tim Graham <timograham@…>]

In 4a6d3f25:

[2.2.x] Fixed #30295 -- Fixed max_lengths.tests.MaxLengthORMTests when run in isolation.

Backport of 5a92bb0725e07068b260364ef66466f126000b0b from master.