Refs #26840 -- Corrected SQLite connection mocking in a setup_databases() test.

The test was expecting connections used by DiscoverRunner.setup_databases()
to be the ones defined in django.test.runner but this doesn't hold true
since this method was made a proxy of django.test.utils.setup_databases.

This broke the TransactionTestCase.serialized_rollback feature in the test
suite because calls to create_db_test() cleared the test data persisted on
connections objects.

Added an assertions to prevent this from happening again.

1 files changed, 22 insertions, 10 deletions

diff --git a/tests/test_runner/tests.py b/tests/test_runner/tests.py
index c95bd8f106..477398da20 100644
--- a/tests/test_runner/tests.py
+++ b/tests/test_runner/tests.py
@@ -247,6 +247,17 @@ class SQLiteInMemoryTestDbs(TransactionTestCase):
     @unittest.skipUnless(all(db.connections[conn].vendor == 'sqlite' for conn in db.connections),
                          "This is an sqlite-specific issue")
     def test_transaction_support(self):
+        # Assert connections mocking is appropriately applied by preventing
+        # any attempts at calling create_test_db on the global connection
+        # objects.
+        for connection in db.connections.all():
+            create_test_db = mock.patch.object(
+                connection.creation,
+                'create_test_db',
+                side_effect=AssertionError("Global connection object shouldn't be manipulated.")
+            )
+            create_test_db.start()
+            self.addCleanup(create_test_db.stop)
         for option_key, option_value in (
                 ('NAME', ':memory:'), ('TEST', {'NAME': ':memory:'})):
             tested_connections = db.ConnectionHandler({
@@ -259,16 +270,17 @@ class SQLiteInMemoryTestDbs(TransactionTestCase):
                     option_key: option_value,
                 },
             })
-            with mock.patch('django.db.connections', new=tested_connections):
-                with mock.patch('django.test.testcases.connections', new=tested_connections):
-                    other = tested_connections['other']
-                    DiscoverRunner(verbosity=0).setup_databases()
-                    msg = ("DATABASES setting '%s' option set to sqlite3's ':memory:' value "
-                           "shouldn't interfere with transaction support detection." % option_key)
-                    # Transaction support should be properly initialized for the 'other' DB
-                    self.assertTrue(other.features.supports_transactions, msg)
-                    # And all the DBs should report that they support transactions
-                    self.assertTrue(connections_support_transactions(), msg)
+            with mock.patch('django.test.utils.connections', new=tested_connections):
+                other = tested_connections['other']
+                DiscoverRunner(verbosity=0).setup_databases()
+                msg = (
+                    "DATABASES setting '%s' option set to sqlite3's ':memory:' value "
+                    "shouldn't interfere with transaction support detection." % option_key
+                )
+                # Transaction support is properly initialized for the 'other' DB.
+                self.assertTrue(other.features.supports_transactions, msg)
+                # And all the DBs report that they support transactions.
+                self.assertTrue(connections_support_transactions(), msg)
 
 
 class DummyBackendTest(unittest.TestCase):