Hi! I just wanted to propose a method for this package that does not require any special JavaScript code to work. This method uses the WebDriver's executeAsyncScript function to attach an actual event listener.

This is the basic function:

use Facebook\WebDriver\Exception\ScriptTimeoutException;
use Facebook\WebDriver\Exception\TimeoutException;
use Laravel\Dusk\Browser;

function (string $name, ?int $seconds = null): Browser {
    /** @var \Laravel\Dusk\Browser $this */
    $seconds = is_null($seconds) ? $this::$waitSeconds : $seconds;

    try {
        $this->driver->manage()
            ->timeouts()
            ->setScriptTimeout($seconds);

        $this->driver->executeAsyncScript("
            const done = () => arguments[0]();
            document.addEventListener('inertia:{$name}', done, { once: true });
        ");
    } catch (ScriptTimeoutException $e) {
        throw new TimeoutException("Waited {$seconds} seconds for an Inertia '{$name}' event.");
    }

    return $this;
}

I created a mixin class that can be used with Browser::mixin():

<?php

use Closure;
use Facebook\WebDriver\Exception\ScriptTimeoutException;
use Facebook\WebDriver\Exception\TimeoutException;
use Laravel\Dusk\Browser;

/** @mixin \Laravel\Dusk\Browser */
class InertiaEventsMixin
{
    public function waitForInertia(?int $seconds = null): Closure
    {
        return fn (?int $seconds = null) => $this->waitForInertiaEvent('navigate', $seconds);
    }

    public function waitForInertiaError(?int $seconds = null): Closure
    {
        return fn (?int $seconds = null) => $this->waitForInertiaEvent('error', $seconds);
    }

    public function waitForInertiaFinish(?int $seconds = null): Closure
    {
        return fn (?int $seconds = null) => $this->waitForInertiaEvent('finish', $seconds);
    }

    public function waitForInertiaInvalid(?int $seconds = null): Closure
    {
        return fn (?int $seconds = null) => $this->waitForInertiaEvent('invalid', $seconds);
    }

    public function waitForInertiaSuccess(): Closure
    {
        return fn (?int $seconds = null) => $this->waitForInertiaEvent('success', $seconds);
    }

    public function waitForInertiaEvent(): Closure
    {
        return function (string $name, ?int $seconds = null): Browser {
            /** @var \Laravel\Dusk\Browser $this */
            $seconds = is_null($seconds) ? $this::$waitSeconds : $seconds;

            try {
                $this->driver->manage()
                    ->timeouts()
                    ->setScriptTimeout($seconds);

                $this->driver->executeAsyncScript("
                    const done = () => arguments[0]();
                    document.addEventListener('inertia:{$name}', done, { once: true });
                ");
            } catch (ScriptTimeoutException $e) {
                throw new TimeoutException("Waited {$seconds} seconds for an Inertia '{$name}' event.");
            }

            return $this;
        };
    }
}

Then in my testing service provider:

\Laravel\Dusk\Browser::mixin(new InertiaEventsMixin);

I'd be happy to provide a pull request if you are interested.

Anyways, thanks for maintaining this package!

Cheers from Germany, Michael