Welcome to your fourth unit for this course, dedicated to practicing Test-Driven Development (TDD), utilizing Ruby and RSpec. We're going to continue building our ShoppingCart system by integrating even more features into our class.

In this course, the emphasis is on hands-on practice, where you'll receive requirements through tests, one at a time. Your task is to write tests AND implement code that makes each test pass, simulating a real-world TDD environment. Where I wrote the tests for you last time, this time it's all up to you!

Remember to use the core concepts of the Red-Green-Refactor cycle while completing these coding exercises. I'm still here to help! Just ask.

This section will cover additional features and enhancements for our ShoppingCart class. As you write your test cases and implement the corresponding functionality, keep the requirements below in mind:

• Description: Removing an item that does not exist in the cart should raise an exception, indicating the item is not found.
• Details
  • Support item removal through a remove_item(item_id) method.
  • Ensure the method raises an appropriate error message if an item does not exist in the cart.
• Examples: Attempting to remove an item with item_id: '999' from the cart should raise an exception with the message 'Item not found'.

Ruby
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1class ShoppingCart
2  attr_reader :items
3
4  def initialize
5    @items = []
6  end
7
8  # Existing methods ...
9
10  def remove_item(id)
11    item = @items.find { |i| i[:id] == id }
12    raise 'Item not found' unless item
13
14    if item[:quantity] > 1
15      item[:quantity] -= 1
16    else
17      @items.delete(item)
18    end
19  end
20end
21
22# Example usage
23cart = ShoppingCart.new
24begin
25  cart.remove_item('999') # Attempt to remove an item that doesn't exist
26rescue RuntimeError => e
27  puts e.message # Output: "Item not found"
28end

• Description: When a percentage discount is applied, the total price of the items in the cart should reflect this discount.
• Details
  • Use the apply_discount(percentage) method to apply a percentage discount to the total.
  • Ensure get_total() returns the discounted price after applying the discount.
• Examples: Applying a 10% discount to an item with a total price of 100 should result in a new total of 90.

Ruby
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1class ShoppingCart
2  # Existing methods ...
3
4  def apply_discount(percentage)
5    discount_factor = (100 - percentage) / 100.0
6    @discounted_total = total * discount_factor
7  end
8
9  def total
10    @discounted_total || @items.sum { |item| item[:price] * item[:quantity] }
11  end
12end
13
14# Example usage
15cart = ShoppingCart.new
16cart.add_item({ id: '1', name: 'Book', price: 100 })
17cart.apply_discount(10)
18puts cart.total # Output: 90

• Description: When the total price of items in the cart exceeds $150, a bulk discount of 10% should be applied to the total.
• Details
  • If the total exceeds 150, a 10% discount should be applied automatically.
  • The get_total() method should return the discounted total when applicable.
• Examples: Adding an item { 'item_id': '1', 'name': 'Book', 'price': 200 } should result in a total of 180 after applying the bulk discount.

Ruby
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1class ShoppingCart
2  # Existing methods ...
3
4  def total
5    base_total = @items.sum { |item| item[:price] * item[:quantity] }
6    if base_total > 150
7      base_total * 0.9
8    else
9      base_total
10    end
11  end
12end
13
14# Example usage
15cart = ShoppingCart.new
16cart.add_item({ id: '1', name: 'Book', price: 200 })
17puts cart.total # Output: 180

• Description: The cart should be able to remove all items, resetting the item count and total price to zero.
• Details
  • Implement a clear() method to remove all items from the cart.
  • Ensure get_item_count() returns 0 after clearing.
  • Verify get_total() is 0 after clearing.
• Examples: If there are multiple items in the cart, calling clear() should leave the count as 0 and the total as 0.

Ruby
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1class ShoppingCart
2  # Existing methods ...
3
4  def clear
5    @items.clear
6  end
7
8  def item_count
9    @items.sum { |item| item[:quantity] }
10  end
11end
12
13# Example usage
14cart = ShoppingCart.new
15cart.add_item({ id: '1', name: 'Book', price: 50 })
16cart.clear
17puts cart.item_count # Output: 0
18puts cart.total      # Output: 0

• Description: When the quantity of an item in the cart is updated, the item count and total price should reflect the updated quantity.
• Details
  • Allow item quantities to be updated using an update_quantity(item_id, quantity) method.
  • Ensure get_item_count() returns the correct count after updating the quantity.
  • Update get_total() to return the correct total price after updating the quantity.
• Examples: Updating the quantity of { 'item_id': '1', 'name': 'Book', 'price': 10 } from 2 to 3 should result in a count of 3 and a total of 30.

Ruby
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1class ShoppingCart
2  # Existing methods ...
3
4  def update_quantity(id, quantity)
5    item = @items.find { |i| i[:id] == id }
6    raise 'Item not found' unless item
7
8    item[:quantity] = quantity
9  end
10end
11
12# Example usage
13cart = ShoppingCart.new
14cart.add_item({ id: '1', name: 'Book', price: 10 }, 2)
15cart.update_quantity('1', 3)
16puts cart.item_count # Output: 3
17puts cart.total      # Output: 30

In this unit, you explored the design of test cases for a new ShoppingCart class, focusing on essential features like handling an empty cart, adding items, managing item quantities, and removing items. Now it’s your turn to ensure that the described functionality is implemented by writing comprehensive test cases and ensuring that the tests pass with the least amount of code using Ruby and RSpec.

As you undertake these exercises, remember to engage in the Red-Green-Refactor cycle. Be sure to practice writing tests first and do not write implementation code unless the test asks for it.

Red! Green! Refactor!