Thanks Adam! That makes sense to me - I believe Redis transactions are atomic by default so the `cas` method wouldn't apply there. I took a look at the LocMemCache code, and I think that the need for cas in this instance also doesn't exist - because the code uses a threading Lock() to prevent race conditions that cas addresses, see
https://github.com/django/django/blob/main/django/core/cache/backends/locmem.py#L38. Perhaps for testing we could simply implement a `cas` method for `LocMemCache` that simply calls `LocMemCache.get`?
I'd be happy to implement the cas() method for both Memcached backends and the dummy method for LocMemCache if that makes sense!