Expose the capybara session in the ruby API

This allows pages that require authentication to be benchmarked

README.md

@@ -61,11 +61,14 @@ Server response times will be reported if the application is a ruby/rack applica
 You can programatically run the benchmarks. Simply specify the URL and
 optionally the amount of runs.
 
+Here is an example of running a benchmark in chrome looping around 3 times.
+
 ```ruby
 
 require 'wbench'
 
-results = WBench::Benchmark.run('https://www.desktoppr.co/', :loops => 3, :browser => :chrome) # => WBench::Results
+benchmark = WBench::Benchmark.new('https://www.desktoppr.co/', :browser => :chrome)
+results   = benchmark.run(3) # => WBench::Results
 
 results.app_server # =>
   [25, 24, 24]
@@ -89,6 +92,31 @@ results.latency # =>
   "ssl.google-analytics.com"=>[497, 14, 14], "www.desktoppr.co"=>[191, 210, 203]}
 ```
 
+### Benchmarking authenticated pages
+
+Benchmarking authenticated pages is possible using the ruby API. The API
+provides direct access to the selenium session. The session allows us to visit
+a login page before our test page, for example:
+
+```ruby
+require 'wbench'
+
+benchmark = WBench::Benchmark.new('https://www.desktoppr.co/dashboard', :browser => :chrome)
+benchmark.before_each do
+  visit 'https://www.desktoppr.co/login'
+  fill_in 'Login', :with => 'mario'
+  fill_in 'Password', :with => 'super secret'
+  click_button 'Log In'
+end
+
+results = benchmark.run(3) # => WBench::Results
+```
+
+Please note that by visiting pages before each run, your browser may cache some
+assets. This means that when the benchmark is run against the authenticated
+page, some assets may be loaded from the cache, and the result may appear
+quicker than an uncahed visit.
+
 ### Gisting results
 
 You can install the [Github gist gem](https://github.com/defunkt/gist) and pipe in the results of wbench

lib/wbench/benchmark.rb

@@ -9,9 +9,14 @@ def initialize(url, options = {})
       @browser = Browser.new(url, options)
     end
 
+    def before_each(&blk)
+      @before_each = blk
+    end
+
     def run(loops)
       Results.new(@url, loops).tap do |results|
         loops.times do
+          @browser.run(&@before_each)
           @browser.visit { results.add(app_server_results, browser_results, latency_results) }
         end
       end

lib/wbench/browser.rb

@@ -3,7 +3,6 @@ class Browser
     attr_accessor :url
 
     def initialize(url, options = {})
-
       Capybara.register_driver(CAPYBARA_DRIVER) do |app|
         http_client         = Selenium::WebDriver::Remote::Http::Default.new
         http_client.timeout = CAPYBARA_TIMEOUT
@@ -32,6 +31,10 @@ def evaluate_script(script)
       session.evaluate_script(script)
     end
 
+    def run(&blk)
+      session.instance_eval(&blk) if block_given?
+    end
+
     private
 
     def add_selenium_args(options, arg)