public function testExampleFromDoc()
{
$m = new Model_User();
$m->addField('salary', ['default' => 1000]);
$this->assertEquals(false, isset($m['salary']));
// false
$this->assertEquals(1000, $m['salary']);
// 1000
// Next we load record from $db
$m->data = ['salary' => 2000];
$this->assertEquals(2000, $m['salary']);
// 2000 (from db)
$this->assertEquals(false, isset($m['salary']));
// false, was not changed
$m['salary'] = 3000;
$this->assertEquals(3000, $m['salary']);
// 3000 (changed)
$this->assertEquals(true, isset($m['salary']));
// true
unset($m['salary']);
// return to original value
$this->assertEquals(2000, $m['salary']);
// 2000
$this->assertEquals(false, isset($m['salary']));
// false
}