Add unittest

[mammatus95]

Add unit test for the php code

composer require --dev phpunit/phpunit

<?php
class Calculator {
    public function add($a, $b) {
        return $a + $b;
    }

    public function subtract($a, $b) {
        return $a - $b;
    }
}

<?php
use PHPUnit\Framework\TestCase;

require_once 'Calculator.php';

class CalculatorTest extends TestCase {
    public function testAdd() {
        $calculator = new Calculator();
        $result = $calculator->add(2, 3);
        $this->assertEquals(5, $result);
    }

    public function testSubtract() {
        $calculator = new Calculator();
        $result = $calculator->subtract(5, 3);
        $this->assertEquals(2, $result);
    }
}