madlib.ex

defmodule Madlib do

  @default_io :erlang.group_leader

  def main(_, device \\ @default_io) do
    noun = prompt device, "noun"
    verb = prompt device, "verb"
    adjective = prompt device, "adjective"
    adverb = prompt device, "adverb"

    sentence = assemble(noun: noun, verb: verb, adjective: adjective, adverb: adverb)
    IO.puts(device, sentence)
  end

  def prompt(device \\ @default_io, message) do
    IO.gets(device, "Enter a #{message}: ")
    |> String.strip
  end

  def assemble noun: noun, verb: verb, adjective: adjective, adverb: adverb do
    "Do you #{verb} your #{adjective} #{noun} #{adverb}?"
  end
end

madlib_test.exs

defmodule MadlibTest do
  use ExUnit.Case

  test "prompt asks me for stuff?" do
    {:ok, pid} = StringIO.open("something I entered\n", capture_prompt: true)
     assert Madlib.prompt(pid, "prompt") == "something I entered"
     {input, output} = StringIO.contents(pid)

     assert input == ""
     assert output == "Enter a prompt: "
  end

  test "assemble sentence" do
    assert "Do you verb your adjective noun adverb" ==
      Madlib.assemble noun: "noun", verb: "verb", adjective: "adjective", adverb: "adverb"
  end

  test "main asks for many things" do
    input = """
    dog
    walk
    blue
    quickly
    """
    {:ok, pid} = StringIO.open(input)

    Madlib.main [], pid

    {input, output} = StringIO.contents(pid)
    assert input == ""
    assert output == "Do you walk your blue dog quickly?\n"
  end
end