Shopping Cart System with Kotlin, TDD, and JUnit

Introduction to the Shopping Cart System

Welcome to your third unit of this course dedicated to practicing Test Driven Development (TDD) utilizing Kotlin and JUnit . We will begin building a new system; this time, we'll focus on creating a shopping cart system with a variety of features. In this course, emphasis is placed 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. Unlike previous exercises, where tests were supplied, this time you're in charge! Remember to utilize the core concepts of the Red-Green-Refactor cycle while working through these exercises. Assistance is available, so don't hesitate to ask for help.

Requirements for ShoppingCart Class

The following requirements outline the foundational functionality of the ShoppingCart class, providing step-by-step guidance to build and test its key features while practicing TDD principles. Each requirement focuses on a specific aspect of the shopping cart's behavior, ensuring a comprehensive and modular approach to its development and testing.

1. Starting with an Empty Cart

Description : When a new ShoppingCart is created in Kotlin, it should start without any items, and the total price should be zero. Details Initialize a new shopping cart using the ShoppingCart constructor. Ensure the method getItemCount() returns 0 for an empty cart. Verify the method getTotal() returns 0 for the initial state. Examples : A newly created cart should have an item count of 0 and a total price of 0 . Kotlin class ShoppingCart {private val items = mutableListOf<Item>() fun getItemCount(): Int = items.size fun getTotal(): Double = items.sumOf { it.price * it.quantity }} JUnit Test Example: Kotlin import org.junit.jupiter.api.Assertions.assertEquals import org.junit.jupiter.api.Test class ShoppingCartTest {@Test fun newlyCreatedCartShouldHaveZeroItemsAndZeroTotal() {val cart = ShoppingCart() assertEquals(0, cart.getItemCount()) assertEquals(0.0, cart.getTotal())}}

2. Adding a Single Item

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Kotlin

data class Item(val id: String, val name: String, val price: Double, val quantity: Int = 1)

class ShoppingCart {
    private val items = mutableListOf<Item>()

    fun addItem(item: Item) {
        items.add(item)
    }

    fun getItemCount(): Int = items.size

    fun getTotal(): Double = items.sumOf { it.price * it.quantity }
}

Kotlin

class ShoppingCartTest {
    @Test
    fun addingASingleItemShouldIncreaseItemCountAndTotalPrice() {
        val cart = ShoppingCart()
        cart.addItem(Item("1", "Book", 10.0))
        assertEquals(1, cart.getItemCount())
        assertEquals(10.0, cart.getTotal())
    }
}

Kotlin

class ShoppingCartTest {
    @Test
    fun addingMultipleDistinctItemsShouldUpdateItemCountAndTotalPrice() {
        val cart = ShoppingCart()
        cart.addItem(Item("1", "Book", 10.0))
        cart.addItem(Item("2", "Pen", 5.0))
        assertEquals(2, cart.getItemCount())
        assertEquals(15.0, cart.getTotal())
    }
}

Kotlin

class ShoppingCartTest {
    @Test
    fun addingMultipleQuantitiesOfTheSameItemShouldUpdateItemCountAndTotalPrice() {
        val cart = ShoppingCart()
        cart.addItem(Item("1", "Book", 10.0, 3))
        assertEquals(3, cart.getItemCount())
        assertEquals(30.0, cart.getTotal())
    }
}

Kotlin

class ShoppingCart {
    private val items = mutableListOf<Item>()

    fun addItem(item: Item) {
        items.add(item)
    }

    fun removeItem(id: String) {
        val item = items[id]
        if (item != null) {
            if (item.getQuantity() > 1) {
                item.setQuantity(item.getQuantity() - 1)
            } else {
                items.remove(id)
            }
        }
    }

    fun getItemCount(): Int = items.sumOf { it.quantity }

    fun getTotal(): Double = items.sumOf { it.price * it.quantity }
}

Kotlin

class ShoppingCartTest {
    @Test
    fun removingAnItemShouldDecreaseItemCountAndUpdateTotalPrice() {
        val cart = ShoppingCart()
        cart.addItem(Item("1", "Book", 10.0, 2))
        cart.removeItem("1")
        assertEquals(0, cart.getItemCount())
        assertEquals(0.0, cart.getTotal())
    }
}

Introduction to the Shopping Cart System

Requirements for ShoppingCart Class

1. Starting with an Empty Cart

2. Adding a Single Item

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3. Adding Multiple Items

4. Handling Multiple Quantities of the Same Item

5. Removing an Item

Summary and Preparation for Practice