<?php

declare(strict_types=1);

namespace Tests;

use DateTime;
use PHPUnit\Framework\MockObject\MockObject;
use PHPUnit\Framework\TestCase;

class ExampleTest extends TestCase
{
    /**
     * @var DateTime&MockObject
     */
    private $property;

    public function testExample(): void
    {
        $this->property = $this->createMock(DateTime::class);
        $this->property->expects(self::once())->method('format');
        $this->property->format('Y');
    }
}

-    /**
-     * @var DateTime&MockObject
-     */
-    private $property;
+    private ?MockObject $property = null;