How to test if memcache is working?
You can enable the memcache_admin module and this will provide a stats page at /admin/reports/memcache, where you can see the number of sets and gets, hits and misses percentages and how much of the allocated memory is in use.

On the server, you can run this from the command line (assuming port 11211):

echo stats | nc 127.0.0.1 11211