api_signature.rb

require File.expand_path('../exceptions', __FILE__)

# Supports the following matchers:
#
#  describe '/api/account.json' do
#    subject { json_response }
#    before { get '/api/account.json' }
#    it { should have_json(:email).of_type(String) }
#    it { should have_json(:posts).of_type(Array).inside_of('account') }
#    it { should have_json(:review).of_type(Hash).inside_of('account/profile') }
#  end
#
RSpec::Matchers.define :have_json do |name|
  diffable

  match do |json|
    begin
      @obj = value_at_json_path(json, @path)["#{name}"]
      @obj != nil && (@type_class.present? ? @obj.kind_of?(@type_class) : true)
    rescue Response::Matchers::MissingPathError
      false
    end
  end

  chain :of_type do |type_class|
    @type_class = type_class
  end

  chain :inside_of do |path|
    @path = path
  end

  failure_message_for_should do |json|
    message = "expected JSON signature to include attribute '#{name}'"
    message << %( of type #{@type_class}) if @type_class
    message << %( at path "#{@path}") if @path
    message << %(, but it was #{@obj.inspect})
    message
  end

  failure_message_for_should_not do |json|
    message = "expected JSON signature to exclude attribute '#{name}'"
    message << %( of type #{@type_class}) if @type_class
    message << %( at path "#{@path}") if @path
    message << %(, but it was #{@obj.inspect})
    message
  end

  description do
    message = "contain the JSON signature for '#{name.to_s}'"
    message << %( of type #{@type_class}) if @type_class.present?
    message << %( at path "#{@path}") if @path.present?
    message
  end

# Begin internal helpers

  def value_at_json_path(json, path)
    return json unless path

    json_path_to_keys(path).inject(json) do |value, key|
      case value
      when Hash, Array then value.fetch(key){ missing_json_path!(path) }
      else missing_json_path!(path)
      end
    end
  end

  def json_path_to_keys(path)
    path.split("/").map{|k| k =~ /^\d+$/ ? k.to_i : k }
  end

  def missing_json_path!(path)
    raise Response::Matchers::MissingPathError.new(path)
  end
end

Output looks like

:public is no longer used to avoid overloading Module#public, use :public_folder instead
        from /Users/justinsmestad/.rbenv/versions/1.9.3-p0/lib/ruby/gems/1.9.1/gems/resque-1.19.0/lib/resque/server.rb:12:in `<class:Server>'
Run filtered including {:locations=>{"./spec/api/account/profiles_api_spec.rb"=>[28]}}

/v1/account.json
  profile updates
    the return payload
      should contain the JSON signature for 'biography' of type String

Finished in 17.28 seconds
1 example, 0 failures