I'm pretty certain that the parameter to expect() is a regexp, which means that $ would be the end-of-line marker, instead of a literal $. Try escaping it with a backslash.

As an aside, it would help if you could include more of the surrounding code. Specifically where you set up the session, and the data that you're actually sending to the send() and expect() calls. It would be best if you reduced it to a "least-common-denominator" snippet that could be run and exhibits the problem.

bbfu
Black flowers blossum
Fearless on my breath