[2.2.x] Made test table cleanup in OperationTestBase more robust.

Some non-unique constraint names were added in
b69f8eb04c which resulted in failures
depending on the order in which tests were run.

Backport of 62b8596616 from master.

tests/migrations/test_multidb.py

@@ -122,13 +122,16 @@ class MultiDBOperationTests(OperationTestBase):
             self.assertEqual(Pony.objects.count(), 0)
 
     @override_settings(DATABASE_ROUTERS=[MigrateNothingRouter()])
-    def test_run_sql(self):
+    def test_run_sql_migrate_nothing_router(self):
         self._test_run_sql("test_mltdb_runsql", should_run=False)
 
     @override_settings(DATABASE_ROUTERS=[MigrateWhenFooRouter()])
-    def test_run_sql2(self):
+    def test_run_sql_migrate_foo_router_without_hints(self):
         self._test_run_sql("test_mltdb_runsql2", should_run=False)
-        self._test_run_sql("test_mltdb_runsql2", should_run=True, hints={'foo': True})
+
+    @override_settings(DATABASE_ROUTERS=[MigrateWhenFooRouter()])
+    def test_run_sql_migrate_foo_router_with_hints(self):
+        self._test_run_sql('test_mltdb_runsql3', should_run=True, hints={'foo': True})
 
     def _test_run_python(self, app_label, should_run, hints=None):
         with override_settings(DATABASE_ROUTERS=[MigrateEverythingRouter()]):
@@ -156,10 +159,13 @@ class MultiDBOperationTests(OperationTestBase):
             self.assertEqual(Pony.objects.count(), 0)
 
     @override_settings(DATABASE_ROUTERS=[MigrateNothingRouter()])
-    def test_run_python(self):
+    def test_run_python_migrate_nothing_router(self):
         self._test_run_python("test_mltdb_runpython", should_run=False)
 
     @override_settings(DATABASE_ROUTERS=[MigrateWhenFooRouter()])
-    def test_run_python2(self):
+    def test_run_python_migrate_foo_router_without_hints(self):
         self._test_run_python("test_mltdb_runpython2", should_run=False)
-        self._test_run_python("test_mltdb_runpython2", should_run=True, hints={'foo': True})
+
+    @override_settings(DATABASE_ROUTERS=[MigrateWhenFooRouter()])
+    def test_run_python_migrate_foo_router_with_hints(self):
+        self._test_run_python('test_mltdb_runpython3', should_run=True, hints={'foo': True})

tests/migrations/test_operations.py

@@ -22,6 +22,24 @@ class OperationTestBase(MigrationTestBase):
     Common functions to help test operations.
     """
 
+    @classmethod
+    def setUpClass(cls):
+        super().setUpClass()
+        cls._initial_table_names = frozenset(connection.introspection.table_names())
+
+    def tearDown(self):
+        self.cleanup_test_tables()
+        super().tearDown()
+
+    def cleanup_test_tables(self):
+        table_names = frozenset(connection.introspection.table_names()) - self._initial_table_names
+        with connection.schema_editor() as editor:
+            with connection.constraint_checks_disabled():
+                for table_name in table_names:
+                    editor.execute(editor.sql_delete_table % {
+                        'table': editor.quote_name(table_name),
+                    })
+
     def apply_operations(self, app_label, project_state, operations, atomic=True):
         migration = Migration('name', app_label)
         migration.operations = operations
@@ -51,26 +69,6 @@ class OperationTestBase(MigrationTestBase):
         """
         Creates a test model state and database table.
         """
-        # Delete the tables if they already exist
-        table_names = [
-            # Start with ManyToMany tables
-            '_pony_stables', '_pony_vans',
-            # Then standard model tables
-            '_pony', '_stable', '_van',
-        ]
-        tables = [(app_label + table_name) for table_name in table_names]
-        with connection.cursor() as cursor:
-            table_names = connection.introspection.table_names(cursor)
-            connection.disable_constraint_checking()
-            sql_delete_table = connection.schema_editor().sql_delete_table
-            with transaction.atomic():
-                for table in tables:
-                    if table in table_names:
-                        cursor.execute(sql_delete_table % {
-                            "table": connection.ops.quote_name(table),
-                        })
-            connection.enable_constraint_checking()
-
         # Make the "current" state
         model_options = {
             "swappable": "TEST_SWAP_MODEL",