Unable to local factory while testing in Laravel 5.3

I've got issue, and can't resolve it :(

I'm trying to set data provider for test in Laravel 5.3.

I have a model Task in app/Task.php file.

I have a factory in database/factories/TaskFactory.php:

$factory->define(App\Task::class, function(Faker\Generator $faker) {
    return [
        'description' => $faker->text,
    ];
});

I have a test in tests/TaskTest.php:

class TaskTest extends TestCase
{
    public function tasksDataProvider()
    {
         $tasks = factory(App\Task::class, 10)->create();

         // return task ids here        
    }

    /**
     * @dataProvider tasksDataProvider
     */
    public function testExistingTask($id)
    {
         // do some assertions with $id here
    }
}

When I run phpunit I've got the output:

1) Warning
The data provider specified for 
TaskTest::testExistingTask is invalid.
Unable to locate factory with name [default] [App\Task].

Right now I can write:

class TaskTest extends TestCase
{
    public function testExistingTask()
    {
         $tasks = factory(App\Task::class, 10)->create();
         // do some assertions with task ids here
    }
}

and everything is OK.

How can I make data provider work with factory?