Stub out the actual downloading.

spec/unit/installer/pod_source_installer_spec.rb

@@ -65,6 +65,7 @@ module Pod
           config.sandbox.store_head_pod('BananaLib')
           @spec.source = { :http => 'http://dl.google.com/googleadmobadssdk/googleadmobsearchadssdkios.zip' }
           @spec.source_files = 'GoogleAdMobSearchAdsSDK/*.h'
+          Pod::Downloader::Http.any_instance.stubs(:download_head)
           should.raise Informative do
             @installer.install!
           end.message.should.match /does not support the :head option, as it uses a Http source./