BadMethodCallException: Call to undefined method Illuminate\Database\Query\Builder::createTickets()

I am working on Order-Ticket functionality. Many tickets should ideally be generated for a single order.

Earlier, the responsibility of creating tickets was written inside Order Model and that time it worked fine but now that I am trying to move that responsibility to Ticket model itself, it is not working.

I'll start with the Test file 'TicketTest.php'

<?php
use Illuminate\Foundation\Testing\WithoutMiddleware;
use Illuminate\Foundation\Testing\DatabaseMigrations;
use Illuminate\Foundation\Testing\DatabaseTransactions;
use App\Concert;
use Carbon\Carbon;
use App\Order;

class TicketTest extends TestCase
{
    use DatabaseMigrations;

    /** @test */
    function can_create_multiple_tickets_for_order(){

        $numberOfTickets = 2;

        // Arrange - Create Concert and Order
        $concert = factory(Concert::class)->create(
            [
                'date' => Carbon::parse('December 1, 2016 8:00pm'),
            ]
        );

        $order = $concert->orders()->create([
            'email' => 'abc@gmail.com'
        ]);

        // Act - Create Tickets
        $order->tickets()->createTickets($numberOfTickets); // This line throws call to undefined method.

        // Assert
        $this->assertEquals($numberOfTickets, $order->tickets()->count());

    }
}

'Order.php' Model

<?php

namespace App;

use Illuminate\Database\Eloquent\Model;

class Order extends Model
{
    protected $guarded = [];

    public function tickets()
    {
        return $this->hasMany(Ticket::class);
    }

}

'Ticket.php' Model

<?php

namespace App;

use Illuminate\Database\Eloquent\Model;

class Ticket extends Model
{
    public function createTickets($ticketQuantity){
        foreach(range(1, $ticketQuantity) as $i) {
            $this->create([]);
        }
    }

    public function order(){
        return $this->belongsTo(Order::class);
    }
}

via Chebli Mohamed