derive_line_filters

# File railties/lib/rails/test_unit/runner.rb, line 123
        def derive_line_filters(patterns)
          patterns.flat_map do |file, lines|
            if lines.empty?
              Filter.new(@runnable, file, nil) if file
            else
              lines.map { |line| Filter.new(@runnable, file, line) }
            end
          end
        end