In_place_edit controller and "Missing template" error

Hello, I’ve this action which runs ok from a browser but fails from a
functional test :

def inplace_update
tag = Tag.find(params[:id])
tag.update_attributes!(:name => params[:value])
render :text => tag.name
end

In place editing works like a charm but when I :
def test_inplace_update
xhr :post, :inplace_update, {:id =>2, :name => ‘change_tag’}
end

I get this error “test_inplace_update(AdminTagsControllerTest):
ActionController::MissingTemplate: Missing template
/usr/local/www/ror_dev/config/…/app/views/admin_tags/inplace_update.rhtml”

I don’t understand why the render :text is skipped when under test

Thanks