title: How to handle test_specs that have common sources
body: <p>Using cocoapods version 1.6.0.rc.1 and cocoapods-generate, I have two test_specs like below:</p>
  
  <pre><code>  s.test_spec 'UnitTests' do |test_spec|
      test_spec.requires_app_host = false
      test_spec.source_files = 'MyThing/Tests/Common/**/*.{h,m}'
      test_spec.source_files = 'MyThing/Tests/Unit/**/*.{h,m}'
    end
  
    s.test_spec 'EndToEndUnitTest' do |test_spec|
      test_spec.requires_app_host = true
      test_spec.source_files = 'MyThing/Tests/Common/**/*.{h,m}'
      test_spec.source_files = 'MyThing/Tests/EndToEnd/**/*.{h,m}'
    end
  </code></pre>
  
  <p>both test_specs have the line</p>
  
  <pre><code>    test_spec.source_files = 'MyThing/Tests/Common/**/*.{h,m}'
  </code></pre>
  
  <p>but cocoapods-generate can't figure out which target the common sources belong to, so they are omitted from the project.</p>
  
  <p><strong>How can I define a set of sources that are common across test_specs?</strong></p>