[2.2.x] Fixed #30111 -- Fixed AppRegistryNotReady error with django.contrib.postgres in INSTALLED_APPS.

Regression in e192223ed996ed30fe83787efdfa7f2be6b1a2ee.
Backport of 2804b8d2153505ec49b191db2168302dfb92c3af from master.

2 files changed, 22 insertions, 0 deletions

diff --git a/tests/postgres_tests/integration_settings.py b/tests/postgres_tests/integration_settings.py
new file mode 100644
index 0000000000..c4ec0d1157
--- /dev/null
+++ b/tests/postgres_tests/integration_settings.py
@@ -0,0 +1,5 @@
+SECRET_KEY = 'abcdefg'
+
+INSTALLED_APPS = [
+    'django.contrib.postgres',
+]
diff --git a/tests/postgres_tests/test_integration.py b/tests/postgres_tests/test_integration.py
new file mode 100644
index 0000000000..829b862027
--- /dev/null
+++ b/tests/postgres_tests/test_integration.py
@@ -0,0 +1,17 @@
+import os
+import subprocess
+import sys
+
+from tests.postgres_tests import PostgreSQLSimpleTestCase
+
+
+class PostgresIntegrationTests(PostgreSQLSimpleTestCase):
+    def test_check(self):
+        os.chdir(os.path.dirname(__file__))
+        result = subprocess.run(
+            [sys.executable, '-m', 'django', 'check', '--settings', 'integration_settings'],
+            stdout=subprocess.DEVNULL,
+            stderr=subprocess.PIPE,
+        )
+        stderr = '\n'.join([e.decode() for e in result.stderr.splitlines()])
+        self.assertEqual(result.returncode, 0, msg=stderr)