An example custom RSpec matcher that makes describing expectations on HTTP failures nicer and gives more information when it fails (like the response body)

http_test_spec.rb

require 'spec_helper'

describe "Fun REST API Function" do

  before(:each) do
    @api = FunRestApi.new
  end

  context "when creating a valid widget" do
    it "responds with a success message" do
       response = @api.post(Widget.new("some widget"))
       response.should have_http_status_code '200'
    end
   end
end

spec_helper.rb

RSpec::Matchers.define :have_http_status_code do |status_code|
  match do |http_response|
    http_response.code.should == status_code
  end

  failure_message_for_should do |http_response|
    "Got HTTP status code '#{http_response.code}' but expected '#{status_code}'. \nThe response body was:\n#{http_response.body}"
  end
end

Assuming the API call failed, you'd get an error something like:

 Failure/Error: response.should have_http_status_code '200'
 Got HTTP status code '400' but expected '200'. 
 The response body was:
 <?xml version="1.0" encoding="utf-8"?><ApiError><Code>666</Code><Message>Invalid Widget!</Message></ApiError>

As opposed to the alternative test code:
...
response.code.should == '200'
...

And the corresponding failure message:
Failure/Error: raw_api_response.code.should == '200'
expected: "200",
got: "400" (using ==)