NoteCat/tests/unit/HelloWorldTest.php

<?php
declare(strict_types=1);

namespace Tests\Unit;

use NoteCat\HelloWorld;
use PHPUnit\Framework\TestCase;

/**
 * @covers NoteCat\HelloWorld
 */
final class HelloWorldTest extends TestCase
{
    public function testGetHello(): void
    {
        $hello = new HelloWorld();
        $this->assertSame('Hello world! :3', $hello->getHello());
    }
}