class Test::Unit::Diff::ReadableDiffer

def format_diff_point(from_line, to_line, from_tags, to_tags)
  common = [n_leading_characters(from_line, ?\t),
            n_leading_characters(to_line, ?\t)].min
  common = [common,
            n_leading_characters(from_tags[0, common], " "[0])].min
  from_tags = from_tags[common..-1].rstrip
  to_tags = to_tags[common..-1].rstrip
  tag_deleted([from_line])
  unless from_tags.empty?
    tag_difference(["#{"\t" * common}#{from_tags}"])
  end
  tag_inserted([to_line])
  unless to_tags.empty?
    tag_difference(["#{"\t" * common}#{to_tags}"])
  end
end