module RSpec::Matchers::Pretty

def to_sentence(words)
  return "" unless words
  words = Array(words).map { |w| to_word(w) }
  case words.length
    when 0
      ""
    when 1
      " #{words[0]}"
    when 2
      " #{words[0]} and #{words[1]}"
    else
      " #{words[0...-1].join(', ')}, and #{words[-1]}"
  end
end