Marathon is a fast and platform-independent test runner focused on performance and stability. Marathon offers easy to use platform implementations for Android and iOS as well as an API for use with custom hardware farms. Marathon implements multiple key concepts related to test execution such as test batching, device pools, test sharding, test sorting, preventive retries as well as post-factum retries. By default, most of these are set to conservative defaults but custom configurations are encouraged for those who want to optimize performance and/or stability. Marathon’s primary focus is on full control over the balance between stability of test execution and the overall test run performance.