with_output_file

# File activesupport/lib/active_support/testing/performance.rb, line 149
            def with_output_file
              fname = output_filename

              if new = !File.exist?(fname)
                FileUtils.mkdir_p(File.dirname(fname))
              end

              File.open(fname, 'ab') do |file|
                file.puts(HEADER) if new
                yield file
              end
            end