[1.11.x] Fixed #28498 -- Fixed test database creation with cx_Oracle 6.

Backport of 6784383e93 from master

django/db/backends/oracle/creation.py

@@ -96,6 +96,8 @@ class DatabaseCreation(BaseDatabaseCreation):
                     print("Tests cancelled.")
                     sys.exit(1)
 
+        # Cursor must be closed before closing connection.
+        cursor.close()
         self._maindb_connection.close()  # done with main user -- test user and tablespaces created
         self._switch_to_test_user(parameters)
         return self.connection.settings_dict['NAME']
@@ -180,6 +182,8 @@ class DatabaseCreation(BaseDatabaseCreation):
             if verbosity >= 1:
                 print('Destroying test database tables...')
             self._execute_test_db_destruction(cursor, parameters, verbosity)
+        # Cursor must be closed before closing connection.
+        cursor.close()
         self._maindb_connection.close()
 
     def _execute_test_db_creation(self, cursor, parameters, verbosity, keepdb=False):

docs/releases/1.11.5.txt

@@ -11,3 +11,5 @@ Bugfixes
 
 * Fixed GEOS version parsing if the version has a commit hash at the end (new
   in GEOS 3.6.2) (:ticket:`28441`).
+
+* Fixed test database creation with ``cx_Oracle`` 6 (:ticket:`28498`).

tests/select_for_update/tests.py

@@ -51,6 +51,7 @@ class SelectForUpdateTests(TransactionTestCase):
 
     def end_blocking_transaction(self):
         # Roll back the blocking transaction.
+        self.cursor.close()
         self.new_connection.rollback()
         self.new_connection.set_autocommit(True)
 
@@ -274,7 +275,10 @@ class SelectForUpdateTests(TransactionTestCase):
             finally:
                 # This method is run in a separate thread. It uses its own
                 # database connection. Close it without waiting for the GC.
-                connection.close()
+                # Connection cannot be closed on Oracle because cursor is still
+                # open.
+                if connection.vendor != 'oracle':
+                    connection.close()
 
         status = []
         thread = threading.Thread(target=raw, kwargs={'status': status})