Fixed #32437 -- Fixed cleaning up ALLOWED_HOSTS in LiveServerTestCase on setUpClass() failure.

django/test/testcases.py

@@ -1573,11 +1573,12 @@ class LiveServerTestCase(TransactionTestCase):
             for conn in cls.server_thread.connections_override.values():
                 conn.dec_thread_sharing()
 
+            cls._live_server_modified_settings.disable()
+            super().tearDownClass()
+
     @classmethod
     def tearDownClass(cls):
         cls._tearDownClassInternal()
-        cls._live_server_modified_settings.disable()
-        super().tearDownClass()
 
 
 class SerializeMixin:

tests/servers/tests.py

@@ -9,6 +9,7 @@ from urllib.error import HTTPError
 from urllib.parse import urlencode
 from urllib.request import urlopen
 
+from django.conf import settings
 from django.core.servers.basehttp import WSGIServer
 from django.test import LiveServerTestCase, override_settings
 from django.test.testcases import LiveServerThread, QuietWSGIRequestHandler
@@ -39,6 +40,42 @@ class LiveServerBase(LiveServerTestCase):
         return urlopen(self.live_server_url + url)
 
 
+class FailingLiveServerThread(LiveServerThread):
+    def _create_server(self):
+        raise RuntimeError('Error creating server.')
+
+
+class LiveServerTestCaseSetupTest(LiveServerBase):
+    server_thread_class = FailingLiveServerThread
+
+    @classmethod
+    def check_allowed_hosts(cls, expected):
+        if settings.ALLOWED_HOSTS != expected:
+            raise RuntimeError(f'{settings.ALLOWED_HOSTS} != {expected}')
+
+    @classmethod
+    def setUpClass(cls):
+        cls.check_allowed_hosts(['testserver'])
+        try:
+            super().setUpClass()
+        except RuntimeError:
+            # LiveServerTestCase's change to ALLOWED_HOSTS should be reverted.
+            cls.check_allowed_hosts(['testserver'])
+        else:
+            raise RuntimeError('Server did not fail.')
+        cls.set_up_called = True
+
+    @classmethod
+    def tearDownClass(cls):
+        # Make tearDownClass() a no-op because setUpClass() was already cleaned
+        # up, and because the error inside setUpClass() was handled, which will
+        # cause tearDownClass() to be called when it normally wouldn't.
+        pass
+
+    def test_set_up_class(self):
+        self.assertIs(self.set_up_called, True)
+
+
 class LiveServerAddress(LiveServerBase):
 
     @classmethod