Refine the django.conf module check to see if the settings really are configured (#668)

Some modules, e.g. hypothesis, load some Django modules for their own fixtures.
This means that the `django.conf` module sometimes gets loaded, even though it's
never used (and the settings are not initialized).

This causes unrelated test failures when pytest_django is installed, as
pytest_django considers that having a loaded django.conf means the settings are
set up and ready to be modified. The Django settings object provides a flag to
check this condition, which we now use.

Add a regression test that mimics what hypothesis did which makes pytest-django
fail.

Closes #599.

Author: olasd

pytest_django/lazy_django.py

@@ -15,16 +15,18 @@ def skip_if_no_django():
 
 
 def django_settings_is_configured():
-    # Avoid importing Django if it has not yet been imported
-    if (
-        not os.environ.get("DJANGO_SETTINGS_MODULE")
-        and "django.conf" not in sys.modules
-    ):
-        return False
-
-    # If DJANGO_SETTINGS_MODULE is defined at this point, Django is assumed to
-    # always be loaded.
-    return True
+    """Return whether the Django settings module has been configured.
+
+    This uses either the DJANGO_SETTINGS_MODULE environment variable, or the
+    configured flag in the Django settings object if django.conf has already
+    been imported.
+    """
+    ret = bool(os.environ.get("DJANGO_SETTINGS_MODULE"))
+
+    if not ret and "django.conf" in sys.modules:
+        return sys.modules["django.conf"].settings.configured
+
+    return ret
 
 
 def get_django_version():

tests/test_django_settings_module.py

@@ -406,6 +406,41 @@ def test_cfg(pytestconfig):
     assert r.ret == 0
 
 
+def test_no_ds_but_django_conf_imported(testdir, monkeypatch):
+    """pytest-django should not bail out, if "django.conf" has been imported
+    somewhere, e.g. via hypothesis (#599)."""
+
+    monkeypatch.delenv('DJANGO_SETTINGS_MODULE')
+
+    testdir.makepyfile("""
+        import os
+        import sys
+
+        # line copied from hypothesis/extras/django.py
+        from django.conf import settings as django_settings
+
+        # Don't let pytest poke into this object, generating a
+        # django.core.exceptions.ImproperlyConfigured
+        del django_settings
+
+        from pytest_django.lazy_django import django_settings_is_configured
+
+        def test_django_settings_is_configured():
+            assert django_settings_is_configured() is False
+
+        def test_django_conf_is_imported():
+            assert 'django.conf' in sys.modules
+
+        def test_env():
+            assert 'DJANGO_SETTINGS_MODULE' not in os.environ
+
+        def test_cfg(pytestconfig):
+            assert pytestconfig.option.ds is None
+    """)
+    r = testdir.runpytest_subprocess('-s')
+    assert r.ret == 0
+
+
 def test_no_django_settings_but_django_imported(testdir, monkeypatch):
     """Make sure we do not crash when Django happens to be imported, but
     settings is not properly configured"""