How to assert response code in Rails controller test? - ruby-on-rails

Question

EDIT
Edited to change to a question about the test rather than code, as I see the application behaves correctly.
I'm writing a Rails 3 app which is purely a RESTful web service (i.e. no views). I have a User model, where the username is unqiue
class User < ActiveRecord::Base
validates_uniqueness_of :username
end
In my controller, I have the following code to handle a new user being created:
def create
#user = User.new(ActiveSupport::JSON.decode(request.raw_post))
if #user.save
puts "Added user #{#user.username}"
format.json { render :json => "" }
else
puts "Failed to add user: #{#user.errors.to_json}"
render json: #user.errors, status: :unprocessable_entity
end
end
I then have a functional test which creates a user with the same username as an existing user:
test "should not create user with duplicate username" do
#jim = users(:jim)
post '/users', #jim.to_json, "CONTENT_TYPE" => "application/json"
assert_response :unprocessable_entity
end
When I run the test, the controller outputs "Failed to add user: {"username":["has already been taken"]}" as expected, but the test fails:
Expected response to be a <:unprocessable_entity>, but was <200>
However, with curl I get the response I expect:
curl -i -X POST -d '{"username": "james", "email": "test#test.com" }'
HTTP/1.1 422
{"username":["has already been taken"]}
So where am I going wrong with the assertion in the test?

Answer 1

You probably should use respond_with. It will take care of lots of REST logic, including setting status codes.
Also, Rails may be overkill for an application that's just a REST service. You might want to consider Sinatra instead.

Answer 2

The reason was that I'd switched to using RackTest to allow me to post JSON in the body (i.e. not as a form parameter.) As a result, I should have been making assertions on last_response (the RackTest MockResponse used in the post call) instead of using assert_response:
test "should not create user with duplicate username" do
#jim = users(:jim)
post '/users.json', #jim.to_json, "CONTENT_TYPE" => "application/json"
assert_status :unprocessable_entity
end
def assert_status(expected_status)
assert_equal last_response.status, Rack::Utils.status_code(expected_status)
end
I am quite surprised assert_response :success passes when no methods have been called which yield a value for #response. If that assertion failed, or threw an exception, it would have been easier to track down my bug, but c'est la vie!