Heterogene iterable queue concept

Queue.php

<?php

namespace App\Core\Pipeline;

class Queue
{
    /**
     * @var \AppendIterator
     */
    private $iterator;

    public function __construct()
    {
        $this->reset();
    }

    public function append($items): void
    {
        $items = is_iterable($items) ? $items : [$items];
        $items = is_array($items) ? new \ArrayIterator($items) : $items;
        $this->iterator->append($items);
    }

    public function next()
    {
        $item = $this->iterator->current();

        $this->iterator->next();

        return $item;
    }

    public function reset(): void
    {
        $this->iterator = new \AppendIterator();
    }

    public function hasNext(): bool
    {
        return $this->iterator->valid();
    }
}

QueueTest.php

<?php

declare(strict_types=1);

namespace App\Tests\Core\Pipeline;

use App\Core\Pipeline\Queue;
use PHPUnit\Framework\TestCase;

class QueueTest extends TestCase
{
    public function testQueue()
    {
        $items = [1, 2];
        $itemGenerator = function() {
            yield 5;
            yield 6;
        };

        $queue = new Queue();
        $this->assertFalse($queue->hasNext());

        $queue->append($items);
        $queue->append(3);

        $this->assertTrue($queue->hasNext());

        $this->assertSame(1, $queue->next());
        $this->assertTrue($queue->hasNext());
        $this->assertSame(2, $queue->next());
        $this->assertTrue($queue->hasNext());
        $this->assertSame(3, $queue->next());
        $this->assertFalse($queue->hasNext());
        $this->assertNull($queue->next());

        $queue->append($itemGenerator());

        $this->assertTrue($queue->hasNext());

        $this->assertSame(5, $queue->next());
        $this->assertTrue($queue->hasNext());
        $this->assertSame(6, $queue->next());
        $this->assertFalse($queue->hasNext());

        $queue->append([]);
        $this->assertFalse($queue->hasNext());
    }

    public function testReset()
    {
        $items = [1, 2];
        $queue = new Queue();
        $queue->append($items);

        $this->assertTrue($queue->hasNext());
        $this->assertSame(1, $queue->next());
        $this->assertTrue($queue->hasNext());

        $queue->reset();
        $this->assertFalse($queue->hasNext());
        $this->assertNull($queue->next());
    }
}