Extend a Laravel Model Factory

FooFactory.php

<?php

// class Admin extends User

$factory->define(App\Admin::class, function (Faker\Generator $faker) {
    return app(Illuminate\Database\Eloquent\Factory::class)
        ->raw(
            Package\Models\User::class,
            [
                'foobar' => 'barbaz',
                'bazqux' => 42
            ]
        );
});

If a package defines a Model Foobar and you class MyFoobar extends Foobar, you probably also want to create a factory(MyFoobar::class) for any fields that your child Model provides or anything that overrides the parent Model's fields.