How To Test PDFs with Capybara Blog post with details: http://pivotallabs.com/test-pdfs-with-capybara/

Gemfile

group :test do
  gem 'rspec-rails'
  gem 'capybara'
  gem 'pdf-reader'
end

pdf_viewing_spec.rb

require 'spec_helper'

feature 'Viewing a PDF' do
  scenario 'User requests the PDF page' do
    visit "/pdfs.pdf"
    convert_pdf_to_page
    page.should have_content("Hi, PDF!") # Passes
  end
end

def convert_pdf_to_page
  temp_pdf = Tempfile.new('pdf')
  temp_pdf << page.source.force_encoding('UTF-8')
  reader = PDF::Reader.new(temp_pdf)
  pdf_text = reader.pages.map(&:text)
  temp_pdf.close
  page.driver.response.instance_variable_set('@body', pdf_text)
end

pdfs_controller.rb

class PdfsController < ApplicationController
  def index
    respond_to do |format|
      format.pdf do
        render :pdf => 'filename.pdf',
          :show_as_html => params[:debug]
      end
    end
  end
end

routes.rb

PdfValidation::Application.routes.draw do
  resources :pdfs, only: [:index]
  root to: "pdfs#index"
end

show.pdf.haml

%h1 Hi, PDF!