public function testDBConnection()
 {
     $this->assertTrue(is_object(self::$connection));
     $this->assertTrue(self::$connection instanceof PDO);
     $connection = DatabaseConnection::close();
     $this->assertNull($connection);
 }
 /**
  * Create a PDO connection if one does not exist.
  *
  * @return void
  */
 public static function connect()
 {
     if (is_null(self::$connection)) {
         self::$connection = DatabaseConnection::connect();
     }
 }