traffic transitions.rb

require "minitest/autorun"

TRAFFIC_TRANSITIONS = {
  "red" => "green",
  "green" => "yellow",
  "yellow" => "red",
}

def is_valid_traffic_sequence(sequence)
  sequence.each_cons(2) do |before, after|
    return false if after != TRAFFIC_TRANSITIONS[before]
  end

  true
end

class TestTransitions < Minitest::Test
  def test_valid    = assert is_valid_traffic_sequence(["red", "green", "yellow", "red", "green"])
  def test_invalid  = refute is_valid_traffic_sequence(["red", "yellow", "green"]);
  def test_empty    = assert is_valid_traffic_sequence([])
end