fix SchemaEditor.alter_db_table() crash when table name is unchanged

Author: timgraham

django_mongodb/features.py

@@ -131,10 +131,6 @@ class DatabaseFeatures(BaseDatabaseFeatures):
         "schema.tests.SchemaTests.test_composed_constraint_with_fk",
         "schema.tests.SchemaTests.test_remove_ignored_unique_constraint_not_create_fk_index",
         "schema.tests.SchemaTests.test_unique_constraint",
-        # pymongo.errors.OperationFailure: Can't rename a collection to itself
-        "migrations.test_operations.OperationTests.test_alter_model_table_noop",
-        "migrations.test_operations.OperationTests.test_rename_model_no_relations_with_db_table_noop",
-        "migrations.test_operations.OperationTests.test_rename_model_with_db_table_rename_m2m",
         # subclasses of BaseDatabaseIntrospection may require a get_constraints() method
         "migrations.test_operations.OperationTests.test_add_func_unique_constraint",
         "migrations.test_operations.OperationTests.test_remove_func_unique_constraint",

django_mongodb/schema.py

@@ -75,4 +75,6 @@ def remove_constraint(self, model, constraint):
         pass
 
     def alter_db_table(self, model, old_db_table, new_db_table):
+        if old_db_table == new_db_table:
+            return
         self.connection.database[old_db_table].rename(new_db_table)