A very small PHP todo list that saves to the database in 32 lines

todo.php

<?php 

//The actual implementation is just this file. Others are usage and tests.

class TodoList extends ArrayObject 
{
    const CREATE = 'CREATE TABLE IF NOT EXISTS tasks (name VARCHAR(32) PRIMARY KEY, status INT)';
    const SELECT = 'SELECT * FROM tasks';
    const INSERT = 'INSERT INTO tasks VALUES (?,?)';
    const UPDATE = 'UPDATE tasks SET status = ? WHERE name = ?';
    const DELETE = 'DELETE FROM tasks WHERE name = ?';

    protected $db;

    public function __construct(PDO $db) 
    {
        $this->db = $db;
        $db->exec(static::CREATE);
        $data = $db->query(static::SELECT, PDO::FETCH_KEY_PAIR)->fetchAll();
        parent::__construct($data, static::ARRAY_AS_PROPS);
    }
    public function offsetSet($task, $status) 
    {
        if (!isset($this[$task]))
            $this->db->prepare(static::INSERT)->execute(array($task, $status));
        else
            $this->db->prepare(static::UPDATE)->execute(array($status, $task));
        parent::offsetSet($task, $status);
    }
    public function offsetUnset($task) 
    {
        $this->db->prepare(static::DELETE)->execute($task);
        parent::offsetUnset($task);
    }
}

usage.php

<?php

$todo = new TodoList(new PDO('mysql:host=localhost;dbName=tasks', 'user', 'pass'));

$todo['Implement the todo list'] = true; //done it!
$todo['Create some tests'] = false;      //not done yet
unset($todo['Make a gist']);             //remove this one

ztests.php

<?php

//Incomplete! Wanna help?

class TodoListTest extends PHPUnit_Framework_TestCase {
    public function setUp($data = array())
    {
        $this->db = $this->getMock('PDO', array('exec', 'query', 'prepare'), array('sqlite::memory:'));
        $this->db->expects($this->once())
             ->method('exec')
             ->with($this->equalTo(TodoList::CREATE, PDO::FETCH_KEY_PAIR));
        $this->stm = $this->getMock('PDOStatement', array('fetchAll', 'execute'));
        $this->stm->expects($this->once())
              ->method('fetchAll')
              ->will($this->returnValue($data));
        $this->db->expects($this->once())
             ->method('query')
             ->with(TodoList::SELECT)
             ->will($this->returnValue($this->stm));
        $this->todo = new TodoList($this->db);
    }
    public function testConstructor() {
        $this->setUp(array('Foo' => true, 'Bar' => false));
        $this->assertCount(2, $this->todo);
        $this->assertEquals($this->todo['Foo'], true);
        $this->assertEquals($this->todo['Bar'], false);
    }
    public function testOffsetSet() {
        $this->stm->expects($this->once())
                  ->method('execute')
                  ->with($this->equalTo(array('Baz', true)));
        $this->db->expects($this->once())
                 ->method('prepare')
                 ->with($this->equalTo(TodoList::INSERT))
                 ->will($this->returnValue($this->stm));
        $this->todo['Baz'] = true;
    }
}