wc.rb

#! /usr/bin/env ruby

require 'bundler/inline'

gemfile do
  gem 'rspec', '3.7', require: false
end

class Program
  def initialize(input)
    @input = input
  end

  def call
    "%8d%8d%8d" % [lines, words, characters]
  end

  def characters
    @input.size
  end

  def lines
    @input.split(/\n/).size
  end

  def words
    @input.split(/\s+/).size
  end
end

if $PROGRAM_NAME == __FILE__
  puts Program.new(STDIN.read).call
  exit
end

require 'rspec'

RSpec.describe Program do
  subject(:program) { described_class.new(input) }
  let(:input) { "line 1\nline 2\nline 3\n" }

  it { expect(program.call).to eq('       3       6      21') }
  it { expect(program.characters).to eq(21) }
  it { expect(program.lines).to eq(3) }
  it { expect(program.words).to eq(6) }
end