derive_line_filters

# File railties/lib/rails/test_unit/line_filtering.rb, line 40
      def derive_line_filters(patterns)
        patterns.flat_map do |file_and_line|
          file, *lines = file_and_line.split(':')

          if lines.empty?
            Filter.new(@runnable, file, nil) if file
          else
            lines.map { |line| Filter.new(@runnable, file, line) }
          end
        end
      end