composer.json

{
    "name": "david/telesales-window",
    "type": "project",
    "require": {
        "phpunit/phpunit": "^7.1"
    }
}

TestingTimeWindow.php

<?php
require 'vendor/autoload.php';

class TelesalesWindow
{
    private $now;

    /**
     * TelesalesWindow constructor.
     *
     * @param \DateTimeImmutable $now
     * @throws \Exception
     */
    public function __construct(DateTimeImmutable $now)
    {
        $this->now = $now;
    }

    /**
     * @return bool
     * @throws \Exception
     */
    public function isWindowOpen()
    {
        $day = (int)$this->now->format('N');
        $hour = (int)$this->now->format('G');

        if ($day === 1 && $hour >= 9) {
            return true;
        } else if ($day >= 2 && $day <= 5) {
            return true;
        } else if ($day === 6 && $hour <= 8) {
            return true;
        }

        return false;
    }
}

use PHPUnit\Framework\TestCase;

class TelesalesWindowTest extends TestCase
{
    /**
     * @return array
     * @throws \Exception
     */
    public function providerData()
    {
        return [
            'Monday 6am' => [
                new DateTimeImmutable('2018-05-14T06:00:00', new DateTimeZone('Europe/London')),
                false
            ],
            'Monday 9am' => [
                new DateTimeImmutable('2018-05-14T09:00:00', new DateTimeZone('Europe/London')),
                true
            ],
            'Tuesday 4pm' => [
                new DateTimeImmutable('2018-05-15T14:00:00', new DateTimeZone('Europe/London')),
                true
            ],
            'Wednesday 5pm' => [
                new DateTimeImmutable('2018-05-16T17:00:00', new DateTimeZone('Europe/London')),
                true
            ],
            'Saturday 7am' => [
                new DateTimeImmutable('2018-05-19T07:00:00', new DateTimeZone('Europe/London')),
                true
            ],
            'Saturday 8am' => [
                new DateTimeImmutable('2018-05-19T08:00:00', new DateTimeZone('Europe/London')),
                true
            ],
            'Saturday 10am' => [
                new DateTimeImmutable('2018-05-19T10:00:00', new DateTimeZone('Europe/London')),
                false
            ],
            'Sunday 11pm' => [
                new DateTimeImmutable('2018-05-20T23:00:00', new DateTimeZone('Europe/London')),
                false
            ],
        ];
    }

    /**
     * @dataProvider providerData
     * @param \DateTimeImmutable $dateTime
     * @param $expected
     * @throws \Exception
     */
    public function testIsWindowOpen(DateTimeImmutable $dateTime, $expected)
    {
        $window = new TelesalesWindow($dateTime);
        $result = $window->isWindowOpen();

        $this->assertEquals($expected, $result);
    }
}