added evaluate_script method to all javascipt drivers for evaluating javascript

lib/capybara/driver/culerity_driver.rb

@@ -70,6 +70,10 @@ class Capybara::Driver::Culerity
     browser.elements_by_xpath(selector).map { |node| Node.new(self, node) }
   end
 
+  def evaluate_script(script)
+    browser.execute_script "#{script}"
+  end
+
 private
 
   def url(path)

lib/capybara/driver/selenium_driver.rb

@@ -84,6 +84,10 @@ class Capybara::Driver::Selenium
     driver.find_elements(:xpath, selector).map { |node| Node.new(self, node) }
   end
 
+  def evaluate_script(script)
+    driver.execute_script "return #{script}"
+  end
+
 private
 
   def url(path)

spec/drivers_spec.rb

@@ -63,20 +63,27 @@ shared_examples_for 'driver' do
 end
 
 shared_examples_for "driver with javascript support" do
+  before { @driver.visit('/with_js') }
+
   describe '#find' do
     it "should find dynamically changed nodes" do
-      @driver.visit('/with_js')
       @driver.find('//p').first.text.should == 'I changed it'
     end
   end
 
   describe '#drag_to' do
     it "should drag and drop an object" do
-      @driver.visit('/with_js')
       draggable = @driver.find('//div[@id="drag"]').first
       droppable = @driver.find('//div[@id="drop"]').first
       draggable.drag_to(droppable)
       @driver.find('//div[contains(., "Dropped!")]').should_not be_nil
     end
   end
+
+  describe "#evaluate_script" do
+    it "should return the value of the executed script" do
+      @driver.evaluate_script('1+1').should == 2
+    end
+  end
+
 end