Shashikant Jagtap has Behat TDD testing tool and the BrowserMob-Proxy to make an automated system that collects performance data on your applications (including load time, recording headers and simulations of network traffic and latency).

BrowserMob Proxy is a utility which is used for capuring HTTP traffic and performance data from the browser. BrowserMob-Proxy adds in essential missing capabilities such as checking HTTP status codes and injecting headers for HTTP Basic Auth. Web Perfomance data can be manually captured by other tools like Firebug or Developers Tools. Using BrowserMob Proxy we can capture perfonace data in HAR format while running automated tests.

He includes the commands you'll need to set up the PHP interface for BrowserMob (PHPBrowserMob) the proxy itself and a sample test and context file that runs some checks against Facebook.