Assertionフレームワークのプロトタイプ（案）

Assertion.php

<?php

class Assertion
{
	private $assertion;
	
	private $valiator;

	public function __construct($assertion, callable $validator)
	{
		$this->assertion = $assertion;
		$this->validator = $validator;
	}
	
	public function assertThat($object)
	{
		$result = call_user_func($this->validator, $object);

		if ( $result === false ) {
			throw new Exception($this->assertion);
		}
	}
}

class AssertionCollection
{
	private $assertions = [];
	
	public function add($assertion, callable $validator)
	{
		$this->assertions[] = new Assertion($assertion, $validator);
	}
	
	public function assertThat($object)
	{
		foreach ( $this->assertions as $assertion ) {
			$assertion->assertThat($object);
		}
	}
}

// ✄ - - - - - - - - - - - - - - - - - - - - - - - - ここからクライアントコード

class ItemEntity
{
	public $price = 0;
}

class ItemAssertion
{
	public static function assertInvariantOf(ItemEntity $item)
	{
		$assertions = new AssertionCollection();
		$assertions->add("Item price is always unsinged", function(ItemEntity $item){
			return ( $item->price > 0 );
		});
		$assertions->assertThat($item);
	}
}

$item = new ItemEntity();
$item->price = -1;
ItemAssertion::assertInvariantOf($item);