Test cases being nonsensical and not testing any real world cases was extremely common even before AI, in my experience.

When teams rely on metrics like code and branch coverage, developers will write tests that only serve to satisfy those metrics. I've seen tests that end with "assert true == true"; they don't test anything and only exist to "cover" a branch.

The situation has improved vastly because of AI. AI agents frequently write good tests that have a real chance of actually catching bugs and improving the reliability of the application.