One thing people do/did with search engines was to observe their ranking stability over time on common queries like "Cats" or "Dogs". If there was any change on

One thing people do/did with search engines was to observe their ranking stability over time on common queries like "Cats" or "Dogs". If there was any change one could meaningfully investigate what has changed. Though this seems a bit more like neuropsychological eval by asking a blackbox(AI) questions.