5-6 /database/seeds/TopicsTableSeeder.php

<?php

use Illuminate\Database\Seeder;

class TopicsTableSeeder extends Seeder
{
    /**
     * Run the database seeds.
     *
     * @return void
     */
    public function run()
    {
        factory(App\Topic::class, 50)->create(['exam_id' => 1]);
    }
}