[Validator] Ensure that the parameter source URLs are used in the Podfile

Didn't work before because `instance_eval` changes the scope of the block

lib/cocoapods/validator.rb

@@ -416,12 +416,10 @@ module Pod
 
     # !@group Helpers
 
-    # @return [Array<Source>] an array of sources used to create the
+    # @return [Array<String>] an array of source URLs used to create the
     #         {Podfile} used in the linting process
     #
-    def sources
-      @sources ||= @source_urls.map { |url| SourcesManager.find_or_create_source_with_url(url) }
-    end
+    attr_reader :source_urls
 
     # @return [Podfile] a podfile that requires the specification on the
     # current platform.
@@ -433,8 +431,9 @@ module Pod
       name     = subspec_name ? subspec_name : spec.name
       podspec  = file.realpath
       local    = local?
+      urls     = source_urls
       podfile  = Pod::Podfile.new do
-        sources.each { |s| source(s.url) }
+        urls.each { |u| source(u) }
         platform(platform_name, deployment_target)
         if local
           pod name, :path => podspec.dirname.to_s

spec/unit/validator_spec.rb

@@ -291,6 +291,14 @@ module Pod
         deployment_target.to_s.should == '5.0'
       end
 
+      it 'repects the source_urls parameter' do
+        sources = %w(https://github.com/CocoaPods/Specs.git https://github.com/artsy/Specs.git)
+        sut = Validator.new(podspec_path, sources)
+        sut.stubs(:validate_url)
+        podfile = sut.send(:podfile_from_spec, :ios, '5.0')
+        podfile.sources.should == sources
+      end
+
       it 'uses xcodebuild to generate notes and warnings' do
         sut = Validator.new(podspec_path, SourcesManager.master.map(&:url))
         sut.stubs(:check_file_patterns)