Fix broken spec & wording of error message.

While working on 658f1237c1596a6f735b7b707130fc0897a1a113 I stumbled
accross another messages that would say 'with error code false', which
doesn't make a lot of sense. Also the plain 'expect raise_error' was
masking another problem with tests. One should always only look for the
exact expected error and not just general for any kind of error.