Add default UIDriver#url implementation

lib/kookaburra/ui_driver.rb

@@ -95,6 +95,15 @@ def initialize(configuration)
       @configuration = configuration
     end
 
+    # Returns the URL for this {UIDriver}.
+    #
+    # This implementation simply returns the
+    # {Kookaburra::Configuration#app_host}, but you might override it if you are
+    # using sub-drivers (see {.ui_driver}) and want them to be addressable.
+    def url
+      @configuration.app_host
+    end
+
     protected
 
     # @attribute [r] address_bar

spec/kookaburra/ui_driver_spec.rb

@@ -35,6 +35,14 @@
     end
   end
 
+  describe '#url' do
+    it 'returns the configured app_host' do
+      config = stub('Configuration', :app_host => 'http://my.example.com')
+      driver = Kookaburra::UIDriver.new(config)
+      driver.url.should == 'http://my.example.com'
+    end
+  end
+
   it_behaves_like :it_can_make_assertions do
     let(:subject) { Kookaburra::UIDriver.new(stub('Configuration')) }
   end