Testing S3 upload with Laravel Medialibrary "The current request does not have a file in a key named"

I'm writing a feature test for a simple photo upload to S3 using Laravel Medialibrary.

This is the test:

/** @test */
public function a_user_can_upload_a_photo()
{
    $this->withoutExceptionHandling();

    Storage::fake('s3');

    $user = factory(User::class)->create();

    $this->signIn($user);

    $this->post( route('users.update.photo', [
        $user,
        'photo' => UploadedFile::fake()->image('photo.jpeg', 500, 500)->size(1000),
    ]));

    $this->assertEquals(1, Media::all()->count());

    Storage::disk('s3')->assertExists('photo.jpeg');
}

and this is the relevant part of the controller method handling the upload:

public function uploadPhoto(User $user, Request $request)
{

    // ...

    try {
        $user->addMediaFromRequest('photo')
            ->preservingOriginal()
            ->toMediaCollection('user-photo');

    } catch (\Exception $e) {
        dd($e);
        Log::debug('User photo upload: ' . $e);

    }

    return redirect(route('users.edit.profile', $user));
}

The error catched there with dd($e) is

The current request does not have a file in a key named photo

I actually can test out that the error message is true with putting right in front of the try-catch:

dd($request->has('photo')); === true

but

dd($request->hasFile('photo')); === false

So I do not attach my mock file properly as a file to the request obviously, but I can't figure out how to do that and every example around my online searches suggest doing the test the way I already do.

Any help much appreciated.