The phantomjs tests outputs TAP to console.log (stdout) but doesn't communicate with the testem server.
The ci command just hangs and doesn't do anything.
A useful default would be for it to just print the stdout TAP info.
Take that back, not necessarily a bug. In this case since it's browser tests, the test runner is waiting for the socket.io events to come, which never will. For your case, you just need to get a tap-writing test runner working, let's work on that and this will naturally sort itself out.
Although this begs the question of: if you just want to use testem to run a script which does not report any test results at all (you just want to see its output to stdout or console.log), what should it do in ci mode? Thoughts?
Obsolete now with tap support in browser https://github.com/airportyh/testem/tree/master/examples/tape_example