public function testNumberSub()
{
$price = new Number('1.99');
$subPrice = $price->sub('1.766');
$this->assertEquals(0.22, $subPrice->getNumber());
$this->assertEquals(1.99, $price->getNumber());
$this->assertEquals(0.224, $subPrice->getNumber(3));
$this->assertEquals(0.224, $subPrice->getNumber(-1));
}
