public function testSingleFieldWithNull()
{
$this->specify('Test uniqueness with single field and a null value.', function () {
$validation = new Validation();
$validation->add('deleted', new Uniqueness());
$messages = $validation->validate(null, $this->robot);
expect($messages->count())->equals(1);
$messages = $validation->validate(null, $this->anotherRobot);
expect($messages->count())->equals(1);
$messages = $validation->validate(null, $this->deletedRobot);
expect($messages->count())->equals(0);
});
}