rspec complex custom matchers

have_form.rb

module CustomUiMatchers
  class HaveForm

    def initialize(action, scope, &block)
      @action, @scope, @block = action, scope, block
    end

    def matches?(response, &block)
      @block = block if block
      response.should @scope.have_tag('form[action=?]', @action) do |form|
        @block.call.matches?(form)
      end
    end

    def failure_message
      "expected response to contain a form with '#{@action}' action but it didn't"
    end

    def negative_failure_message
      "expected response to not contain a form with '#{@action}' action but it did"
    end
  end

  # :call-seq:
  #   response.should have_form(action)
  #   response.should_not have_form(action)
  #
  # Accepts form action value
  #
  # == Examples
  #
  #   response.should have_form(users_path)
  # or
  #   response.should have_form(users_path) do
  #     with_field_set 'Personal Information' do
  #       with_text_field 'First Name', 'user[first_name]'
  #     end
  #   end
  def have_form(action, &block)
    HaveForm.new(action, self, &block)
  end

end

new.html.haml_spec.rb

require File.dirname(__FILE__) + '/../../spec_helper'

describe "/users/new" do
  def mock_user(stubs = {})
    @mock_user ||= mock_model(User, stubs)
  end

  before do
    assigns[:user] = mock_user(:new_record? => true)
  end

  it "should have form to create a new user" do
    render '/users/new'
    response.should have_form(users_path) do
      with_field_set 'Personal Information' do
        with_text_field 'wrong', 'wrong'                 # there is no such field on the form. but it passes
        with_text_field 'First Name', 'user[first_name]'
      end
    end
  end
end

with_field_set.rb

module CustomUiMatchers
  class WithFieldSet

    def initialize(scope, legend = nil, &block)
      @scope, @legend, @block = scope, legend, block
    end
 
    def matches?(form, &block)
      @block = block if block
      form.should @scope.have_tag('fieldset') do
        @scope.with_tag('legend', @legend) if @legend
        @scope.with_tag('ol') do |ol|
          @block.call.matches?(ol)
        end
      end
    end
 
    def failure_message
      "expected response to contain a fieldset but it didn't"
    end
 
    def negative_failure_message
      "expected response to not contain a fieldset but it did"
    end
  end
 
  def with_field_set(legend = nil, &block)
    WithFieldSet.new(self, legend, &block)
  end

end

with_input.rb

module CustomUiMatchers
  class WithInput

    def initialize(label, param_name, type, scope)
      @label, @param_name, @type, @scope = label, param_name, type, scope
    end
 
    def matches?(ol)
      ol.should @scope.have_tag 'li' do
        @scope.with_tag('label', @label)
        @scope.with_tag("input[type=#{@type}][name=?]", @param_name)
      end
    end
 
    def failure_message
      "expected response to contain input[type=#{@type}][name=#{@param_name}] labelled '#{@label}' but it didn't"
    end
 
    def negative_failure_message
      "expected response to not contain input[type=#{@type}][name=#{@param_name}] labelled '#{@label}' but it did"
    end
  end
 
  def with_text_field(label, param_name)
    WithInput.new(label, param_name, 'text', self)
  end

  def with_password_field(label, param_name)
    WithInput.new(label, param_name, 'password', self)
  end

end