Testing File Uploads fails at validation

At my wits end here. No idea why this isn't working. Everything works great from the browser, the code allows me to upload videos successfully, and it throws the validation error if no file is provided. This test works fine without the validation rule. What the heck am I missing?

Thank you

controller

    public function store(Request $request)
    {

        $this->validate($request, [
            'channel_id' => 'required|exists:channels,id',
            'title' => 'required',
            'video' => 'required',
            'body' => 'required',
        ]);

        $file = $request->file('video')->store('videos');

        $video = Video::create([
            'user_id' => auth()->id(),
            'channel_id' => request('channel_id'),
            'title' => request('title'),
            'body' => request('body'),
            'path' => $file
        ]);

        return redirect($video->link());
    }

** test **

 function an_authenticated_user_can_create_new_videos()
   {
       $this->signIn();


       $video = make('App\Video');
       $rawVideo = prepareVideoUpload($video);
       

       $response = $this->post('/videos', $rawVideo);


       $this->get($response->headers->get('Location'))
           ->assertSee($video->title);
   }

** factory **

$factory->define(App\Video::class, function($faker)
{

    return [
        'user_id' => function() {
            return factory('App\User')->create()->id;
        },
        'channel_id' => function() {
            return factory('App\Channel')->create()->id;
        },
        'title' => $faker->sentence,
        'body' => $faker->paragraph,
        'path' => 'test.mp4'
    ];
});

helper function

function prepareVideoUpload(\App\Video $video)
{
    $rawVideo = $video->toArray();

    $path  = '/tmp/test.mp4';
    $mimeType = 'video/mp4';
    $file = new \Symfony\Component\HttpFoundation\File\UploadedFile ($path, 'test.mp4', $mimeType, 383631, null, false);


    $rawVideo['video'] = $file;

    return $rawVideo;
}