test for delivery date

Calculation.php

<?php

namespace App\Components\DeliveryCalculation;


use App\Components\Interfaces\DeliveryMethod\DeliveryMethodInterface;

class Calculation implements CalculationInterface, \JsonSerializable
{
    /**
     * @var
     */
    private $price;
    /**
     * @var \DateInterval
     */
    private $time;
    /**
     * @var DeliveryMethodInterface
     */
    private $deliveryMethod;
    /**
     * @var \DateTimeImmutable
     */
    private $today;

    public function __construct(
        $price,
        \DateInterval $time,
        \DateTimeImmutable $today,
        DeliveryMethodInterface $deliveryMethod
    )
    {
        $this->price = $price;
        $this->time = $time;
        $this->deliveryMethod = $deliveryMethod;
        $this->today = $today;
    }

    /**
     * @return float
     */
    public function getPrice()
    {
        return $this->price;
    }

    /**
     * @return \DateInterval
     */
    public function getDeliveryInterval()
    {
        return $this->time;
    }

    /**
     * @return DeliveryMethodInterface
     */
    public function getDeliveryMethod()
    {
        return $this->deliveryMethod;
    }

    /**
     * Specify data which should be serialized to JSON
     * @link http://php.net/manual/en/jsonserializable.jsonserialize.php
     * @return mixed data which can be serialized by <b>json_encode</b>,
     * which is a value of any type other than a resource.
     * @since 5.4.0
     */
    public function jsonSerialize()
    {
        return [
            'price'          => $this->getPrice(),
            'time'           => $this->getDeliveryInterval(),
            'deliveryMethod' => $this->getDeliveryMethod(),
        ];
    }

    /**
     * @return \DateTimeImmutable
     */
    public function getDeliveryDate()
    {
        // TODO: Implement getDeliveryDate() method.
    }
}

CalculationTest.php

<?php

namespace App\Tests\Components\DeliveryCalculation;

use App\Components\DeliveryCalculation\Calculation;
use App\Components\Interfaces\DeliveryMethod\DeliveryMethodInterface;
use PHPUnit\Framework\TestCase;

class CalculationTest extends TestCase
{
    /**
     * @param string $today
     * @param int $interval
     * @param string $valid
     * @dataProvider getDates
     */
    public function test_getDeliveryDate($today, $interval, $valid)
    {
        $todayDate = new \DateTimeImmutable($today);
        $intervalObject = new \DateInterval("P{$interval}D");
        $validDate = new \DateTimeImmutable($valid);

        $calculation = new Calculation(
            200,
            $intervalObject,
            $todayDate,
            $this->getDeliveryMethod()
        );
        $this->assertEquals(
            $validDate,
            $calculation->getDeliveryDate()
        );
    }

    public function getDates()
    {
        return [
            ['2017-08-16', 2, '2017-08-18'],
            ['2017-08-16', 5, '2017-08-23'],
            ['2017-08-16', 13, '2017-09-04'],
        ];
    }

    public function getDeliveryMethod()
    {
        return $this->getMockBuilder(DeliveryMethodInterface::class)->getMock();
    }
}