RSpec matcher for parsing `response.headers['Content-Type']`

have_content_type.rb

RSpec::Matchers.define :have_content_type do |content_type|
  CONTENT_HEADER_MATCHER = /^(.*?)(?:; charset=(.*))?$/

  chain :with_charset do |charset|
    @charset = charset
  end

  match do |response|
    _, content, charset = *content_type_header.match(CONTENT_HEADER_MATCHER).to_a

    if @charset
      @charset == charset && content == content_type
    else
      content == content_type
    end
  end

  failure_message_for_should do |response|
    if @charset
      "Content type #{content_type_header.inspect} should match #{content_type.inspect} with charset #{@charset}"
    else
      "Content type #{content_type_header.inspect} should match #{content_type.inspect}"
    end
  end

  failure_message_for_should_not do |model|
    if @charset
      "Content type #{content_type_header.inspect} should not match #{content_type.inspect} with charset #{@charset}"
    else
      "Content type #{content_type_header.inspect} should not match #{content_type.inspect}"
    end
  end

  def content_type_header
    response.headers['Content-Type']
  end
end

MIT License

Copyright (c) 2012 James Conroy-Finn

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

my_controller_spec.rb

require 'spec_helper'

class MyController < ApplicationController
  respond_to :json, :only => :json

  def json
    respond_with(:json => 'rocks')
  end
end

MyApp::Application.routes.draw do
  match '/my_controller/json' => 'api_actions#json'
end

describe MyController do
  describe 'GET #json' do
    it 'responds with application/json' do
      get :json, :format => :json
      response.should have_content_type('application/json')
    end
  end
end

Make a gem!