average

average.rb

def average(*values)
  values.inject(:+)/values.size.to_f if !values.empty?
end

test_average.rb

require 'minitest/autorun'
require './average'

class TestAverage < MiniTest::Test

  def test_two_numbers
    assert_equal 6, average(4,8)
    assert_equal 15, average(10, 20)
  end

  def test_three_numbers
    assert_equal 6, average(4,6,8)
  end

  def test_empty
    assert_equal nil, average
  end

  def test_real_number
    assert_equal 7.5, average(5,10)
  end
end