public function testShouldBeImmutable()
{
$p1ArrayMoney = ['EUR' => 100, 'GBP' => 101];
$p2ArrayMoney = ['EUR' => 100];
$p2ArrayCurrency = ['EUR/GBP 1.100'];
$price1 = new Price($p1ArrayMoney);
$price2 = new Price($p2ArrayMoney, $p2ArrayCurrency);
$priceAdd = $price1->add($price2);
$priceMul = $price1->multiply(2);
$this->assertEquals(new Price($p1ArrayMoney), $price1);
$this->assertEquals(new Price($p2ArrayMoney, $p2ArrayCurrency), $price2);
}