`Attempt to read property "form" on null` error in test

 Attempt to read property "form" on null

  at vendor/filament/forms/src/Testing/TestsForms.php:125
    121▕     public function assertFormExists(): Closure
    122▕     {
    123▕         return function (string $name = 'form'): static {
    124▕             /** @var ComponentContainer $form */
  ➜ 125▕             $form = $this->instance()->{$name};

it("needs an existing account user", function () {
    \Pest\Livewire\livewire(CompleteRegistration::class)
        ->fillForm([
            'email' => '[email protected]',
        ])
        ->call('register')
        ->assertRedirect(filament()->getLoginUrl());
});

<?php

namespace App\Filament\Pages\Auth;

use DanHarrin\LivewireRateLimiting\WithRateLimiting;
use Filament\Forms\Form;
use Filament\Http\Middleware\Authenticate;
use Filament\Pages\Page;
use Livewire\Features\SupportRedirects\Redirector;

/**
 * @property-read \Filament\Forms\ComponentContainer $form
 */
class CompleteRegistration extends Page
{
    use WithRateLimiting;

    public ?array $data = [];

    protected static string $view = 'filament.auth.complete-registration';

    protected static string $layout = 'filament-panels::components.layout.simple';

    protected static string | array $withoutRouteMiddleware = [
        Authenticate::class,
    ];

    public function mount(): void
    {
        $this->form->fill([
            // defaults
        ]);
    }

    public function register(): Redirector
    {
        // register
    }

    public function form(Form $form): Form
    {
        return $form
            ->statePath('data')
            ->schema([
                // schema
            ]);
    }

    public function hasLogo(): bool
    {
        return true;
    }
}