Unit tests: fill multiselect manually

$categories = Category::query()->inRandomOrder()->take(3)->get();
expect($this->user->categories->count())->toBe(0);
livewire(EditProfile::class)
    ->fillForm([
        'categories' => $categories, // <--- this place i try to find out
    ])
    ->assertFormSet([
        'categories' => $categories->pluck('name', 'id')->toArray(),  // <--- this place i try to find out
    ])
    ->call('save');
expect($this->user->categories->count())->toBe(3);