So, I heard you need Drupal and memcached running in Travis, right? But you have this "little" issue that Travis/Drupal cannot connect to memcached, something like:
WD memcache: You must enable the PHP memcache (recommended) or [error] memcached extension to use memcache.inc.
WD memcache: Failed to connect to memcache server: 127.0.0.1:11211 [error]
Before you jump into docs and tutorials on how to install memcached in Travis, probably it's already there, you just have to enable.
Simply add a new php.ini file somewhere in your source, for example in travis_scripts/php.ini:
extension = "memcached.so"
and point that from your Travis, for example from your before_install section:
phpenv config-add travis_scripts/php.ini
Or even better, from your setup_environment.sh or equivalent
Your error should have gone now.