Refs #16010 -- Required CSRF_TRUSTED_ORIGINS setting to include the scheme.

tests/check_framework/test_4_0_compatibility.py

@@ -0,0 +1,27 @@
+from django.core.checks import Error
+from django.core.checks.compatibility.django_4_0 import (
+    check_csrf_trusted_origins,
+)
+from django.test import SimpleTestCase
+from django.test.utils import override_settings
+
+
+class CheckCSRFTrustedOrigins(SimpleTestCase):
+
+    @override_settings(CSRF_TRUSTED_ORIGINS=['example.com'])
+    def test_invalid_url(self):
+        self.assertEqual(check_csrf_trusted_origins(None), [
+            Error(
+                'As of Django 4.0, the values in the CSRF_TRUSTED_ORIGINS '
+                'setting must start with a scheme (usually http:// or '
+                'https://) but found example.com. See the release notes for '
+                'details.',
+                id='4_0.E001',
+            )
+        ])
+
+    @override_settings(
+        CSRF_TRUSTED_ORIGINS=['http://example.com', 'https://example.com'],
+    )
+    def test_valid_urls(self):
+        self.assertEqual(check_csrf_trusted_origins(None), [])