Staying OO and Testable while working with a database

Question

What are some OOP strategies for working with a database but keeping things unit testable? Say I have a User class and my production environment works against MySQL. I see a couple possible approaches, shown here using PHP:

1. Pass in a $data_source with interfaces for load() and save(), to abstract the backend source of data. When testing, pass a different data store.

   $user = new User( $mysql_data_source );
   $user->load( 'bob' );
   $user->setNickname( 'Robby' );
   $user->save();
   

2. Use a factory that accesses the database and passes the result row to User's constructor. When testing, manually generate the $row parameter, or mock the object in UserFactory::$data_source. (How might I save changes to the record?)

   class UserFactory {
       static $data_source;
   
       public static function fetch( $username ) {
           $row = self::$data_source->get( [params] );
   
           $user = new User( $row );
           return $user;
       }
   }
   

I have Design Patterns and Clean Code here next to me, but I'm struggling to find applicable concepts.