user.rb

class User
  attr_accessor :first_name, :last_name, :age

  def initialize(first_name, last_name, age)
    @first_name = first_name
    @last_name = last_name
    @age = age
  end

  def full_name
    "#{@first_name} #{@last_name}"
  end

  def greet(name)
    "#{first_name}: Hola #{name}"
  end

  def adult?
    @age >= 18
  end
end

user_test.rb

require 'minitest/autorun'
require './user'

class UserTest < Minitest::Test
  def setup
    @user = User.new("Paola", "Garcia", 15)
  end

  def test_full_name
    assert_equal "Paola Garcia", @user.full_name
  end

  def test_greet
    assert_equal "Paola: Hola Leydis", @user.greet("Leydis")
  end

  def test_adult
    @user.age = 18
    assert @user.adult?
  end

  def test_no_adult
    @user.age = 17
    assert_equal false, @user.adult?
  end
end