Fix possible AttributeError: module 'django.core.mail' has no attribute 'outbox' errors (#1187)

This error happened when the `locmem` email backend is not configured and
the `_dj_autoclear_mailbox` autouse fixture kicked in.

Fix #993

Author: kingbuzzman

pytest_django/plugin.py

@@ -599,7 +599,8 @@ def _dj_autoclear_mailbox() -> None:
 
     from django.core import mail
 
-    del mail.outbox[:]
+    if hasattr(mail, "outbox"):
+        mail.outbox.clear()
 
 
 @pytest.fixture()
@@ -608,12 +609,13 @@ def mailoutbox(
     _dj_autoclear_mailbox: None,
 ) -> list[django.core.mail.EmailMessage] | None:
     """A clean email outbox to which Django-generated emails are sent."""
-    if not django_settings_is_configured():
-        return None
+    skip_if_no_django()
 
     from django.core import mail
 
-    return mail.outbox  # type: ignore[no-any-return]
+    if hasattr(mail, "outbox"):
+        return mail.outbox  # type: ignore[no-any-return]
+    return []
 
 
 @pytest.fixture()

tests/conftest.py

@@ -30,11 +30,13 @@ def _marker_apifun(
     extra_settings: str = "",
     create_manage_py: bool = False,
     project_root: str | None = None,
+    create_settings: bool = True,
 ):
     return {
         "extra_settings": extra_settings,
         "create_manage_py": create_manage_py,
         "project_root": project_root,
+        "create_settings": create_settings,
     }
 
 
@@ -135,14 +137,18 @@ def django_pytester(
 
     # Copy the test app to make it available in the new test run
     shutil.copytree(str(app_source), str(test_app_path))
-    tpkg_path.joinpath("the_settings.py").write_text(test_settings)
+    if options["create_settings"]:
+        tpkg_path.joinpath("the_settings.py").write_text(test_settings)
 
     # For suprocess tests, pytest's `pythonpath` setting doesn't currently
     # work, only the envvar does.
     pythonpath = os.pathsep.join(filter(None, [str(REPOSITORY_ROOT), os.getenv("PYTHONPATH", "")]))
     monkeypatch.setenv("PYTHONPATH", pythonpath)
 
-    monkeypatch.setenv("DJANGO_SETTINGS_MODULE", "tpkg.the_settings")
+    if options["create_settings"]:
+        monkeypatch.setenv("DJANGO_SETTINGS_MODULE", "tpkg.the_settings")
+    else:
+        monkeypatch.delenv("DJANGO_SETTINGS_MODULE", raising=False)
 
     def create_test_module(test_code: str, filename: str = "test_the_test.py") -> Path:
         r = tpkg_path.joinpath(filename)

tests/test_fixtures.py

@@ -825,3 +825,62 @@ def mocked_make_msgid(*args, **kwargs):
     result = django_pytester.runpytest_subprocess("--tb=short", "-vv", "-s")
     result.stdout.fnmatch_lines(["*test_mailbox_inner*", "django_mail_dnsname_mark", "PASSED*"])
     assert result.ret == 0
+
+
+@pytest.mark.django_project(
+    create_manage_py=True,
+    extra_settings="""
+    EMAIL_BACKEND = "django.core.mail.backends.dummy.EmailBackend"
+    """,
+)
+def test_mail_auto_fixture_misconfigured(django_pytester: DjangoPytester) -> None:
+    """
+    django_test_environment fixture can be overridden by user, and that would break mailoutbox fixture.
+
+    Normally settings.EMAIL_BACKEND is set to "django.core.mail.backends.locmem.EmailBackend" by django,
+    along with mail.outbox = []. If this function doesn't run for whatever reason, the
+    mailoutbox fixture will not work properly.
+    """
+    django_pytester.create_test_module(
+        """
+        import pytest
+
+        @pytest.fixture(autouse=True, scope="session")
+        def django_test_environment(request):
+            yield
+        """,
+        filename="conftest.py",
+    )
+
+    django_pytester.create_test_module(
+        """
+        def test_with_fixture(settings, mailoutbox):
+            assert mailoutbox == []
+            assert settings.EMAIL_BACKEND == "django.core.mail.backends.dummy.EmailBackend"
+
+        def test_without_fixture():
+            from django.core import mail
+            assert not hasattr(mail, "outbox")
+        """
+    )
+    result = django_pytester.runpytest_subprocess()
+    result.assert_outcomes(passed=2)
+
+
+@pytest.mark.django_project(create_settings=False)
+def test_no_settings(django_pytester: DjangoPytester) -> None:
+    django_pytester.create_test_module(
+        """
+        def test_skipped_settings(settings):
+            assert False
+
+        def test_skipped_mailoutbox(mailoutbox):
+            assert False
+
+        def test_mail():
+            from django.core import mail
+            assert not hasattr(mail, "outbox")
+        """
+    )
+    result = django_pytester.runpytest_subprocess()
+    result.assert_outcomes(passed=1, skipped=2)