public function testSubtract() { $objNumber = new Number(50000); $objNumberToSubtract = new Number(30000); $objNew = $objNumber->subtract($objNumberToSubtract); $this->assertSame(50000, $objNumber->getAmount()); $this->assertSame(30000, $objNumberToSubtract->getAmount()); $this->assertSame(20000, $objNew->getAmount()); }