A ruby version of the Haskell colour problem in seven languages in seven weeks

colours.rb

def colour_combinations(colours=[])
  colours.flat_map{|x| colours.flat_map{|y| x <= y ? [[x, y]] : [] } }
end

require 'minitest/autorun'
require 'minitest/unit'

class TestColours < MiniTest::Unit::TestCase
  
  def test_colour_combinations
    colours = ["black", "white", "blue", "yellow", "red"]

    combinations = colour_combinations(colours)

    assert combinations.include?(["black", "black"])
    assert combinations.include?(["black", "blue"])
    refute combinations.include?(["blue", "black"])
    assert_equal 15, combinations.size
  end

end