How to set up yaml fixtures with UploadedFile (e.g. image) files?

You should use Alice.

Alice is a PHP fixtures generator that allows you to load fixtures from PHP or Yaml files easily and manage uploaded files. Here is a snippet of code that loads some data fixtures from a Doctrine Fixtures class:

<?phpnamespace MyProject\User\Fixtures;use Doctrine\Bundle\FixturesBundle\Fixture;use Doctrine\Common\Persistence\ObjectManager;use Nelmio\Alice\Loader\Yaml;use Nelmio\Alice\ORM\Doctrine;use Symfony\Component\Finder\Finder;class LoadUserData implements FixtureInterface{    public function load(ObjectManager $manager)    {        // load objects from a yaml file        $loader = new \Nelmio\Alice\Loader\Yaml();        $objects = $loader->load(__DIR__.'/users.yml');        $persister = new \Nelmio\Alice\ORM\Doctrine($manager);        $persister->persist($objects);        // Copy images into the legacy application        $fs = $this->container->get('filesystem');        $legacyPath = $this->container->getParameter('legacy_path').'/web/uploads';        $basePath = __DIR__.'/../files';        $finder = \Symfony\Component\Finder\Finder::create()            ->files()            ->in($basePath)            ->ignoreDotFiles(true)            ->ignoreVCS(true)        ;        foreach ($finder as $file) {            if ($file->isFile()) {                $newFile = str_replace($basePath, $legacyPath, $file->getPathname());                $fs->copy($file->getPathname(), $newFile);            }        }    }}

And in your data to load in a YML file :

# users.ymlMyProject\User:    user_1:        firstName: "Albert"        lastName:  "Einstein"        username:  "albert"        email:     "albert.einstein@protonmail.com"

More info here.