Setting the body of a POST request in a Rails integration test
You might try to set the request object's RAW_POST_DATA as you do in a functional test, but this will fail.
The following blog explains the solution:
http://codemonky.com/post/8241251/integration-test-fun
Basically, you do something like this:
body = "this is what i want to post"
post "/path", body, {}