GreeterTest.php

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

use PHPUnit\Framework\TestCase;
use Carbon\Carbon;

class Greeter
{
    /**
     * PHP標準で用意されているDateTimeだと
     * greetに引数なしの場合テストを書くことが難しいのでCarbonを使う
     */
    public function greet()
    {
        $currentDateTime = Carbon::now();
        $hour = (int) $currentDateTime->format('H');

        if (5 <= $hour && $hour < 12) {
            return 'おはようございます';
        } elseif (12 <= $hour && $hour < 18) {
            return 'こんにちは';
        } elseif ((18 <= $hour && $hour <= 23) || (0 <= $hour && $hour < 5)) { // elseでいいよね..
            return 'こんばんは';
        }
    }
}

class GreeterTest extends TestCase
{
    function testGreet()
    {
        $greeter = new Greeter();

        Carbon::setTestNow(Carbon::createFromTime(5, 0, 0));
        $this->assertEquals('おはようございます', $greeter->greet());
        Carbon::setTestNow(Carbon::createFromTime(11, 59, 59));
        $this->assertEquals('おはようございます', $greeter->greet());

        Carbon::setTestNow(Carbon::createFromTime(12, 0, 0));
        $this->assertEquals('こんにちは', $greeter->greet());
        Carbon::setTestNow(Carbon::createFromTime(17, 59, 59));
        $this->assertEquals('こんにちは', $greeter->greet());

        Carbon::setTestNow(Carbon::createFromTime(18, 0, 0));
        $this->assertEquals('こんばんは', $greeter->greet());
        Carbon::setTestNow(Carbon::createFromTime(23, 59, 59));
        $this->assertEquals('こんばんは', $greeter->greet());
        Carbon::setTestNow(Carbon::createFromTime(24, 0, 0));
        $this->assertEquals('こんばんは', $greeter->greet());
        Carbon::setTestNow(Carbon::createFromTime(0, 0, 0));
        $this->assertEquals('こんばんは', $greeter->greet());
        Carbon::setTestNow(Carbon::createFromTime(4, 59, 59));
        $this->assertEquals('こんばんは', $greeter->greet());

        // 後始末
        // 強制設定した時刻をリセット
        Carbon::setTestNow();
    }

    /**
     * @dataProvider currentDateTimeProvider
     * データプロバイダを利用して記述を簡略化する
     */
    function testGreetWithDataProvider($expected, $hour, $minute, $second)
    {
        $greeter = new Greeter();

        Carbon::setTestNow(Carbon::createFromTime($hour, $minute, $second));
        $this->assertEquals($expected, $greeter->greet());

        // 後始末
        // 強制設定した時刻をリセット
        Carbon::setTestNow();
    }

    public function currentDateTimeProvider()
    {
        return [
            ['おはようございます', 5, 0, 0],
            ['おはようございます', 11, 59, 59],
            ['こんにちは', 12, 0, 0],
            ['こんにちは', 17, 59, 59],
            ['こんばんは', 18, 0, 0],
            ['こんばんは', 23, 59, 59],
            ['こんばんは', 24, 0, 0],
            ['こんばんは', 0, 0, 0],
            ['こんばんは', 4, 59, 59],
        ];
    }
}