PHP Testing Jargon Episode 5 - Class not found

I'm stuck around two minutes in with the following error. VSCode indicates that App\Quiz is imported in QuizTest.php, but running both vendor/bin/phpunit tests --colors and vendor/bin/phpunit tests/QuizTest.php --colors gives me the same error. Any thoughts on what's going wrong?

There was 1 error:

1) Tests\QuizTest::it_consists_of_questions
Error: Class 'App\Quiz' not found

C:\testing-jargon\example-2\tests\QuizTest.php:13

ERRORS!
Tests: 1, Assertions: 0, Errors: 1.

QuizTest.php

<?php

namespace Tests;

use App\Quiz;
use PHPUnit\Framework\TestCase;

class QuizTest extends TestCase
{
	/** @test */
	public function it_consists_of_questions()
	{
		$quiz = new Quiz;

		$quiz->addQuestion(
			new Question('What is 2 + 2?', 4)
		);

		$this->assertCount(1, $quiz->questions());
	}
}

Quiz.php

<?php

namespace App;

class Quiz
{

}