public function testMultiply() { $objNumber = new Number(50000); $objNumberToMultiplyWith = new Number(30000); $objNew = $objNumber->multiply($objNumberToMultiplyWith); $this->assertSame(50000, $objNumber->getAmount()); $this->assertSame(30000, $objNumberToMultiplyWith->getAmount()); $this->assertSame(150000, $objNew->getAmount()); }