Efficient configuration for a purely temporary, small Oracle installation
You can either "drop user test_user cascade;", then create the user again with all needed grants and objects, or drop the database and restore a backup of the database while it is empty. Depending on the number of tables, indexes and constraints one of the two methods will be faster. The more tables, indexes and constraints, the more likely just dropping the database and restoring a backup of the empty database will be faster.