Yield day with plenty of iterators + RSpec

acronym.rb

def acronym(sentence)
  return sentence.split.map { |word| word[0] }.join.upcase
end

acronym_spec.rb

require_relative '../acronym.rb'

describe "#acronym" do
  it "returns an empty string when passed an empty string" do
    actual = acronym("")
    expected = ""
    expect(actual).to eq(expected) # passes if `actual == expected`
  end

  it "returns the acronym on downcased sentences" do
    actual = acronym("working from home")
    expected = "WFH"
    expect(actual).to eq(expected)
  end

  it "returns the acronym on upcased sentences" do
    actual = acronym("AWAY FROM KEYBOARD")
    expected = "AFK"
    expect(actual).to eq(expected)
  end
end

encrypt.rb

def encrypt(text)
  # we need array of 26 letters from the alphabet (capitalized)
  # split the unencrpyted text in letters
  # iterate each letter (check its a letter)
  # take letter and shift it by 3 letters backwards
  # join the array
  alphabet = ("A".."Z").to_a
  text.upcase.split("").map do |letter|
    index = alphabet.index(letter)
    index.nil? ? " " : alphabet[index - 3]
  end.join
end

encrypt_spec.rb

require_relative '../encrypt.rb'

describe "#encrypt" do
  it "return an empty string when passed an emptry string" do
    actual = encrypt("")
    expected = ""
    expect(actual).to eq(expected)
  end

  it "returns the 3-letter backward-shifted text" do
    actual = encrypt("THE QUICK BROWN FOX JUMPS OVER THE LAZY DOG")
    expected = "QEB NRFZH YOLTK CLU GRJMP LSBO QEB IXWV ALD"
    expect(actual).to eq(expected)
  end
end

Don't forget to put the spec files in a spec directory so that it looks like this