There are two features of the gem that are making it difficult for me to use with formtastic and cucumber.
First issue is that it assumes @object_name is a string and accesses it directly. At least when I use formtastic, @object_name appears to be assigned a Symbol value. Therefore, I think calling @object_name.to_s would be more robust in AutoCompleteFormBuilderHelper.
Second issue is that when I try to test using cucumber, I try to find the field by its label. It appears the gem now uses the object's unique identifier to generate its html id where it used to simply assign an idea as would be done for a normal text field. The latter behavior would allow it to function in tests like a regular text field.
module AutoCompleteFormBuilderHelper/text_field_with_auto_complete
this (elsif !(@object_name.to_s =~ /[]$/))
should be (elsif (@object_name.to_s =~ /[]$/)) .e.q. without negation ('!')