In this recent post to the SitePoint PHP blog Bruno Skvorc looks at using a popular tool from the Apache project, Apache Bench (or just "ab") to stress-test your application.
There’s no telling when your app might attract a throng of visitors at once. [...] Regardless of the reason, massive influxes of visitors are a double-edged sword: they get you what you always wanted – a chance to prove your worth to a large chunk of the internet’s population – but also often bring with them what you always feared: absolute downtime. [Some] platforms usually offer plugins that can optimize your application while it’s up, so you can fine tune it as you go along, but why not try and predict issues while still developing locally and save yourself time, money and effort in the long run?
He bases the testing off of a Laravel Homestead virtual machine instance and tests a simple "hello world" PHP page to minimize any overhead from other processing. He includes the commands to make a simple ab request and mentions the kinds of request it provides on completion. He moves on from there to something a bit more complex - an actual Laravel-based application using the default "HomeController" and "showWelcome" action/view combination.