I've made a macro for the Illuminate\Testing\TestResponse class that I put into the TestCase.php file which is a part of pingcrm-svelte. I currently use this short macro in basically all HTTP tests for Inertia related endpoints in Laravel, so unless I am doing something wrong, it can be considered quite helpful. Take a look:

use Illuminate\Testing\TestResponse;
use Illuminate\Foundation\Testing\TestCase as BaseTestCase;
use Inertia\Testing\Assert as InertiaAssert;
// use PHPUnit\Framework\Assert;

abstract class TestCase extends BaseTestCase {
  protected function setUp(): void {

    TestResponse::macro('assertInertiaComponent', function ($component) {
      return $this->assertStatus(200)->assertInertia(function (
        InertiaAssert $page,
      ) use ($component) {

To use it inside the HTTP test with PHPUnit it can now be employed like this:

public function test_user_can_see_items() {

It can definitely be made different or better, but hey, it's a good start for me.