Unknown formatter "paragraph" when unit testing

I was learning Let's Build A Forum with Laravel and TDD. There's an error occured when i do the unit test.

function it_has_an_owner(){
    $reply = Reply::factory()->create();

    $this->assertInstanceOf('App\Models\User', $reply->owner);
}

There was 1 error:

1. Tests\Unit\ReplyTest::it_has_an_owner InvalidArgumentException: Unknown formatter "paragraph"

D:\work\laracasts_forum\vendor\fakerphp\faker\src\Faker\Generator.php:250 D:\work\laracasts_forum\vendor\fakerphp\faker\src\Faker\Generator.php:230 D:\work\laracasts_forum\vendor\fakerphp\faker\src\Faker\Generator.php:287 D:\work\laracasts_forum\database\factories\ReplyFactory.php:33 D:\work\laracasts_forum\vendor\laravel\framework\src\Illuminate\Database\Eloquent\Factories\Factory.php:380 D:\work\laracasts_forum\vendor\laravel\framework\src\Illuminate\Database\Eloquent\Factories\Factory.php:359 D:\work\laracasts_forum\vendor\laravel\framework\src\Illuminate\Database\Eloquent\Factories\Factory.php:343 D:\work\laracasts_forum\vendor\laravel\framework\src\Illuminate\Database\Eloquent\Concerns\GuardsAttributes.php:157 D:\work\laracasts_forum\vendor\laravel\framework\src\Illuminate\Database\Eloquent\Factories\Factory.php:348 D:\work\laracasts_forum\vendor\laravel\framework\src\Illuminate\Database\Eloquent\Factories\Factory.php:316 D:\work\laracasts_forum\vendor\laravel\framework\src\Illuminate\Database\Eloquent\Factories\Factory.php:228 D:\work\laracasts_forum\tests\Unit\ReplyTest.php:15

And the Reply factor is:

class ReplyFactory extends Factory { /** * The name of the factory's corresponding model. * * @var string */ protected $model = Reply::class;

/**
 * Define the model's default state.
 *
 * @return array
 */
public function definition()
{
    return [
        'thread_id' => function(){
            return Thread::factory()->create()->id;
        },
        'user_id' => function(){
            return User::factory()->create()->id;
        },
        'body' => $this->faker->paragraph,
    ];
}

}

Why is this happening?