Example of stubbing dependencies in Ruby unit test

main.rb

require 'bundler/inline'

gemfile do
  source "https://rubygems.org"
  gem "money", require: "money"
  gem "minitest"
  gem "mocha"
end

# Calculate the current lifetime value of a user based on how much content they have generated
class LTVCalculator
  attr_reader :user
  private :user

  # Average post adds 5c of value
  POSTS_VALUE = Money.from_cents 5
  private_constant :POSTS_VALUE

  # Average image adds 10c of value
  IMAGES_VALUE = Money.from_cents 10
  private_constant :IMAGES_VALUE

  # Average video adds 50c of value
  VIDEOS_VALUE = Money.from_cents 50
  private_constant :VIDEOS_VALUE

  def initialize(user)
    @user = user
  end

  # The tota LTV for given User
  # @return [Money]
  def total_ltv
    total_posts_value + total_images_value + total_videos_value
  end

  private

  def total_posts_value
    (user.posts_count * POSTS_VALUE)
  end

  def total_images_value
    (user.images_count * IMAGES_VALUE)
  end

  def total_videos_value
    (user.videos_count * VIDEOS_VALUE)
  end
end

require 'minitest/autorun'
require 'mocha/minitest'

class LTVCalculatorTest < Minitest::Test
  def test_total_ltv_awards_5c_per_post
    user = stub('User', posts_count: 2, images_count: 0, videos_count: 0)
    assert_equal Money.from_dollars(0.10), LTVCalculator.new(user).total_ltv
  end

  def test_total_ltv_awards_1oc_per_image
    user = stub('User', posts_count: 0, images_count: 2, videos_count: 0)
    assert_equal Money.from_dollars(0.20), LTVCalculator.new(user).total_ltv
  end

  def test_total_ltv_awards_50c_per_video
    user = stub('User', posts_count: 0, images_count: 0, videos_count: 2)
    assert_equal Money.from_dollars(1.00), LTVCalculator.new(user).total_ltv
  end

  def test_total_ltv_returns_the_sum_value_of_all_user_content
    user = stub('User', posts_count: 2, images_count: 2, videos_count: 2)
    assert_equal Money.from_dollars(1.30), LTVCalculator.new(user).total_ltv
  end
end