TY - GEN N2 - This paper reports the results of the deployment of Rich-State Simulated Populations at Meta for both automated and manual testing. We use simulated users (aka test users) to mimic user interactions and 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. ID - discovery10199776 UR - https://doi.org/10.1145/3639477.3639729 EP - 12 TI - Enhancing Testing at Meta with Rich-State Simulated Populations Y1 - 2024/05/31/ AV - public KW - Software Testing KW - Cyber Cyber Digital Twins KW - Simulation-Based Testing KW - Machine Learning PB - ACM A1 - Alshahwan, Nadia A1 - Blasi, Arianna A1 - Bojarczuk, Kinga A1 - Ciancone, Andrea A1 - Gucevska, Natalija A1 - Harman, Mark A1 - Krolikowski, Michal A1 - Rojas, Rubmary A1 - Martac, Dragos A1 - Schellaert, Simon A1 - Ustiuzhanina, Kate A1 - Harper, Inna A1 - Jia, Yue A1 - Lewis, Will N1 - This version is the author accepted manuscript. For information on re-use, please refer to the publisher?s terms and conditions. SP - 1 ER -