Fixed #20681 -- Prevented teardown_databases from attempting to tear down aliases

Thanks simonpercivall.

django/test/runner.py

@@ -272,15 +272,16 @@ def setup_databases(verbosity, interactive, **kwargs):
         test_databases.items(), dependencies):
         test_db_name = None
         # Actually create the database for the first connection
-
         for alias in aliases:
             connection = connections[alias]
-            old_names.append((connection, db_name, True))
             if test_db_name is None:
                 test_db_name = connection.creation.create_test_db(
                         verbosity, autoclobber=not interactive)
+                destroy = True
             else:
                 connection.settings_dict['NAME'] = test_db_name
+                destroy = False
+            old_names.append((connection, db_name, destroy))
 
     for alias, mirror_alias in mirrored_aliases.items():
         mirrors.append((alias, connections[alias].settings_dict['NAME']))

tests/test_runner/tests.py

@@ -316,6 +316,40 @@ class AliasedDefaultTestSetupTest(unittest.TestCase):
             db.connections = old_db_connections
 
 
+class AliasedDatabaseTeardownTest(unittest.TestCase):
+    def test_setup_aliased_databases(self):
+        from django.db.backends.dummy.base import DatabaseCreation
+
+        runner_instance = runner.DiscoverRunner(verbosity=0)
+        old_db_connections = db.connections
+        old_destroy_test_db = DatabaseCreation.destroy_test_db
+        old_create_test_db = DatabaseCreation.create_test_db
+        try:
+            destroyed_names = []
+            DatabaseCreation.destroy_test_db = lambda self, old_database_name, verbosity=1: destroyed_names.append(old_database_name)
+            DatabaseCreation.create_test_db = lambda self, verbosity=1, autoclobber=False: self._get_test_db_name()
+
+            db.connections = db.ConnectionHandler({
+                'default': {
+                    'ENGINE': 'django.db.backends.dummy',
+                    'NAME': 'dbname',
+                },
+                'other': {
+                    'ENGINE': 'django.db.backends.dummy',
+                    'NAME': 'dbname',
+                }
+            })
+
+            old_config = runner_instance.setup_databases()
+            runner_instance.teardown_databases(old_config)
+
+            self.assertEqual(destroyed_names.count('dbname'), 1)
+        finally:
+            DatabaseCreation.create_test_db = old_create_test_db
+            DatabaseCreation.destroy_test_db = old_destroy_test_db
+            db.connections = old_db_connections
+
+
 class DeprecationDisplayTest(AdminScriptTestCase):
     # tests for 19546
     def setUp(self):