Test edits.

django/db/backends/base/schema.py

@@ -641,7 +641,7 @@ def alter_db_table_comment(self, model, old_db_table_comment, new_db_table_comme
             self.sql_alter_table_comment
             % {
                 "table": self.quote_name(model._meta.db_table),
-                "comment": self.quote_value(new_db_table_comment),
+                "comment": self.quote_value(new_db_table_comment or ""),
             }
         )
 

django/db/migrations/operations/models.py

@@ -560,7 +560,7 @@ def database_backwards(self, app_label, schema_editor, from_state, to_state):
         return self.database_forwards(app_label, schema_editor, from_state, to_state)
 
     def describe(self):
-        return f"Alter {self.name_lower} comment"
+        return f"Alter {self.name} table comment"
 
     @property
     def migration_name_fragment(self):

tests/migrations/test_base.py

@@ -75,6 +75,20 @@ def _get_column_collation(self, table, column, using):
     def assertColumnCollation(self, table, column, collation, using="default"):
         self.assertEqual(self._get_column_collation(table, column, using), collation)
 
+    def _get_table_comment(self, table, using):
+        with connections[using].cursor() as cursor:
+            return next(
+                t.comment
+                for t in connections[using].introspection.get_table_list(cursor)
+                if t.name == table
+            )
+
+    def assertTableComment(self, table, comment, using="default"):
+        self.assertEqual(self._get_table_comment(table, using), comment)
+
+    def assertTableCommentNotExists(self, table, using="default"):
+        self.assertIn(self._get_table_comment(table, using), [None, ""])
+
     def assertIndexExists(
         self, table, columns, value=True, using="default", index_type=None
     ):
@@ -152,31 +166,6 @@ def assertFKExists(self, table, columns, to, value=True, using="default"):
     def assertFKNotExists(self, table, columns, to):
         return self.assertFKExists(table, columns, to, False)
 
-    def _get_column_db_comment(self, table, column, using):
-        return [
-            c.comment
-            for c in self.get_table_description(table, using=using)
-            if c.name == column
-        ][0]
-
-    def assertColumnCommentEquals(self, table, column, column_comment, using="default"):
-        self.assertEqual(
-            self._get_column_db_comment(table, column, using), column_comment
-        )
-
-    def assertColumnCommentNotEquals(
-        self, table, column, column_comment, using="default"
-    ):
-        self.assertNotEqual(
-            self._get_column_db_comment(table, column, using), column_comment
-        )
-
-    def assertColumnCommentExists(self, table, column, using="default"):
-        self.assertTrue(self._get_column_db_comment(table, column, using))
-
-    def assertColumnCommentNotExists(self, table, column, using="default"):
-        self.assertFalse(self._get_column_db_comment(table, column, using))
-
     @contextmanager
     def temporary_migration_module(self, app_label="migrations", module=None):
         """

tests/migrations/test_commands.py

@@ -690,70 +690,6 @@ def test_showmigrations_plan_no_migrations(self):
         )
         self.assertEqual("(no migrations)\n", out.getvalue().lower())
 
-    @skipUnlessDBFeature("supports_comments")
-    @override_settings(
-        MIGRATION_MODULES={"migrations": "migrations.test_migrations_db_comment"}
-    )
-    def test_migrate_db_comment(self):
-        stdout = io.StringIO()
-        call_command(
-            "migrate", "migrations", "0001", verbosity=2, stdout=stdout, no_color=True
-        )
-
-        # The correct tables exist
-        self.assertColumnCommentEquals(
-            "migrations_author", "name", "db comment to name Field"
-        )
-        self.assertColumnCommentNotExists("migrations_author", "slug")
-        self.assertColumnCommentEquals(
-            "migrations_author", "age", "db comment to age Field"
-        )
-        self.assertColumnCommentEquals(
-            "migrations_author", "silly_field", "changed db comment"
-        )
-
-        self.assertColumnCommentNotExists("migrations_tribble", "id")
-        self.assertColumnCommentNotExists("migrations_tribble", "fluffy")
-        self.assertColumnCommentEquals(
-            "migrations_tribble", "bool_field", "new db comment"
-        )
-
-        # Run migrations all the way
-        call_command("migrate", verbosity=0)
-        # The correct tables exist
-        self.assertColumnCommentNotExists("migrations_author", "silly_field")
-        self.assertColumnExists("migrations_author", "rating")
-        self.assertColumnCommentEquals(
-            "migrations_author", "rating", "new comment for rating Column"
-        )
-        self.assertColumnCommentEquals("migrations_book", "author_id", "this is FK")
-
-        # Unmigrate 0002
-        stdout = io.StringIO()
-        call_command(
-            "migrate", "migrations", "0001", verbosity=2, stdout=stdout, no_color=True
-        )
-        # The correct db comment
-        self.assertColumnCommentEquals(
-            "migrations_author", "name", "db comment to name Field"
-        )
-        self.assertColumnCommentNotExists("migrations_author", "slug")
-        self.assertColumnCommentEquals(
-            "migrations_author", "age", "db comment to age Field"
-        )
-        self.assertColumnCommentEquals(
-            "migrations_author", "silly_field", "changed db comment"
-        )
-
-        self.assertColumnCommentNotExists("migrations_tribble", "id")
-        self.assertColumnCommentNotExists("migrations_tribble", "fluffy")
-        self.assertColumnCommentEquals(
-            "migrations_tribble", "bool_field", "new db comment"
-        )
-        # Unmigrate everything
-        call_command("migrate", "migrations", "zero", verbosity=0)
-        call_command("migrate", "migrations", "zero", verbosity=0, database="other")
-
     @override_settings(
         MIGRATION_MODULES={"migrations": "migrations.test_migrations_squashed_complex"}
     )

tests/migrations/test_operations.py

@@ -1922,6 +1922,37 @@ def test_alter_field_add_db_column_noop(self):
                 operation.database_forwards(app_label, editor, new_state, project_state)
         self.assertColumnExists(rider_table, "pony_id")
 
+    @skipUnlessDBFeature("supports_comments")
+    def test_alter_model_table_comment(self):
+        app_label = "test_almotaco"
+        project_state = self.set_up_test_model(app_label)
+        pony_table = f"{app_label}_pony"
+        # Add table comment.
+        operation = migrations.AlterModelTableComment("Pony", "Custom pony comment")
+        self.assertEqual(operation.describe(), "Alter Pony table comment")
+        self.assertEqual(operation.migration_name_fragment, "alter_pony_table_comment")
+        new_state = project_state.clone()
+        operation.state_forwards(app_label, new_state)
+        self.assertEqual(
+            new_state.models[app_label, "pony"].options["db_table_comment"],
+            "Custom pony comment",
+        )
+        self.assertTableCommentNotExists(pony_table)
+        with connection.schema_editor() as editor:
+            operation.database_forwards(app_label, editor, project_state, new_state)
+        self.assertTableComment(pony_table, "Custom pony comment")
+        # Reversal.
+        with connection.schema_editor() as editor:
+            operation.database_backwards(app_label, editor, new_state, project_state)
+        self.assertTableCommentNotExists(pony_table)
+        # Deconstruction.
+        definition = operation.deconstruct()
+        self.assertEqual(definition[0], "AlterModelTableComment")
+        self.assertEqual(definition[1], [])
+        self.assertEqual(
+            definition[2], {"name": "Pony", "db_table_comment": "Custom pony comment"}
+        )
+
     def test_alter_field_pk(self):
         """
         The AlterField operation on primary keys (things like PostgreSQL's