This paper reports the results of the deployment of Rich-State Simulated Populations at Meta for both automated and manual testing. We simulate user interactions using simulated users (aka test users) that acquire state in much the same way that real user accounts acquire state. For automated testing, we present empirical results from deployment on the Facebook, Messenger, and Instagram apps for iOS and Android Platforms. These apps consist of tens of millions of lines of code, communicating with hundreds of millions of lines of backend code, and are
used by over 2 billion people every day. Our results reveal that rich state increases average code coverage by 38%, and endpoint coverage by 61%. More importantly, it also yields an average increase of 115% in the faults found by automated testing. The rich-state test user populations are also deployed in a (continually evolving) Test Universe; a web-enabled simulation platform for privacy-safe manual testing, which has been used by over 21,000 Meta engineers since its deployment in November 2022.