The Example in A Field Guide to Unit Testing series in https://jennycodes.me

unit-testing-example-restaurtant-test.rb

# frozen_string_literal: true

require 'rspec'
require_relative 'restaurant'

RSpec.describe Restaurant::Server do
  describe '#take_order' do
    it 'with French toast passes the order to Cook' do
      expect_any_instance_of(Restaurant::Cook).to receive(:make_french_toast)

      Restaurant::Server.new.take_order('French toast')
    end

    it 'with other orders returns an error message' do
      result = Restaurant::Server.new.take_order('Not French toast')

      expect(result).to be_kind_of String
    end

    it 'with other orders does not pass order to Cook' do
      expect_any_instance_of(Restaurant::Server).not_to receive(:serve)

      Restaurant::Server.new.take_order('Not French toast')
    end
  end

  describe '#serve' do
    it 'returns decorated dish as a string' do
      result = Restaurant::Server.new.serve('French toast is here. Ugh.')

      expect(result).to eq 'Delicious French toast yo!'
    end
  end
end

RSpec.describe Restaurant::Cook do
  describe '#make_french_toast' do
    context 'with ingredients prepared' do
      it 'returns French toast as string' do
        allow(Restaurant::StorageRoom).to receive(:get).with('egg').and_return('egg')
        allow(Restaurant::StorageRoom).to receive(:get).with('bread').and_return('bread')

        result = Restaurant::Cook.new.make_french_toast

        expect(result).to eq 'French toast is here. Ugh.'
      end
    end

    context 'without everything prepared' do
      it 'returns error message - egg' do
        allow(Restaurant::StorageRoom).to receive(:get).with('egg').and_return(nil)
        allow(Restaurant::StorageRoom).to receive(:get).with('bread').and_return('bread')

        result = Restaurant::Cook.new.make_french_toast

        expect(result).to eq 'Oops running out of eggs!'
      end

      it 'returns error message - bread' do
        allow(Restaurant::StorageRoom).to receive(:get).with('egg').and_return('egg')
        allow(Restaurant::StorageRoom).to receive(:get).with('bread').and_return(nil)

        result = Restaurant::Cook.new.make_french_toast

        expect(result).to eq 'Oops running out of bread!'
      end
    end
  end
end

unit-testing-example-restaurtant.rb

module Restaurant
  class Server
    def take_order(dish)
      if dish == 'French toast'
        Cook.new.make_french_toast
      else
        "We only make French toast. Take it or leave it."
      end
    end

    # This method is called when Cook is done cooking the dish.
    def serve(dish)
      decorated_dish = decorate(dish)

      "#{decorated_dish} yo!"
    end

    private

    def decorate(dish_with_murmur)
      dish_name = dish_with_murmur.gsub(' is here. Ugh.', '')
      "Delicious #{dish_name}"
    end
  end

  class Cook
    def make_french_toast
      # [Step 1] Get eggs and bread from StorageRoom
      egg = StorageRoom.get('egg')
      bread = StorageRoom.get('bread')

      # Some error cases handling
      return 'Oops running out of eggs!' unless egg
      return 'Oops running out of bread!' unless bread

      # [Step 2] Making French toast with the eggs and bread
      puts 'Making French toast'

      # [Step 3] Return the plate of French toast as a string
      'French toast is here. Ugh.'
    end
  end

  class StorageRoom
    def self.get(ingredient)
      # We don't really care about the implementation.
      # Just know that it's supposed to return the ingredient if the database has it.
    end

    def self.put(ingredient)
      # We don't really care about the implementation.
      # Just know that it's supposed to insert the ingredient into the database.
    end
  end
end