I was banging my head against the wall when trying to test the sending of an email in a Rails 3 app with Sinatra / Email Spec and getting the following error message:
undefined method `parameters' for #<Mail::UnstructuredField:0x2eceecc>
I was using the latest versions of all the gems in my GemFile and the error did not occur outside of Cucumber. I finally tracked the issue down to the fact that the command line
cucumber in system gems was an old version. This was causing the issue even though the latest cucumber was declared in my GemFile.
I couldn't find anything through Google for the error message so though I would post here incase anyone else runs into the same problem.