def unique_files(dir, dir_files, common_files)
      unique = dir_files - common_files
      if !unique.empty?
        @test_failures << yellowit("\nMissing from directory #{dir}:\n")
        unique.each do |f| 
          failure = "  - #{f}"
          failure << "\n" if unique.last == f
          @test_failures << failure
        end
      end
    end
def unique_files(dir, dir_files, common_files)
      unique = dir_files - common_files
      if !unique.empty?
        @test_failures << yellowit("\nMissing from directory #{dir}:\n")
        unique.each do |f| 
          failure = "  - #{f}"
          failure << "\n" if unique.last == f
          @test_failures << failure
        end
      end
    end
Find files which aren't common to both directories