How to do xml post in test

Rails
1

For my testing of a xml api, I have in my tests

get :xml_api, {:id=>1}, {:user=>User.find(1)}

Say I have a REXML document stored in my_xml, I would expect that I
could do

post :xml_api, {:id=>1}, {:user=>User.find(1)}, my_xml

But it doesn’t work. I’m using rails 1.1.6. Using curl or the web, a
post of xml works fine.