Yes, we have a "pre-call test" module in our client library which is executed as soon as callstats.js is initialized. The test is done with one of our TURN servers (the closest one to the user, based on latency). The pre-call test measures the Media connectivity, RTT, Fractional loss and Throughput from a browser point of view. The pre-call test results can be shown to the end user to inform them about the network quality for WebRTC calls. The results of the pre-call test are displayed in the "Participants" table, on the Conference details tab:
The test is most useful if the user spends some time on the website before actually calling. Please keep in mind that if your service provides a website for the sole purpose of calling, the precall test might not have enough time to be run.