Continue Developing the calculateDiscount Function with Kotlin

Continue Developing the calculateDiscount Function

Welcome to your second lesson, which continues to delve into Test Driven Development (TDD) practices using Kotlin and JUnit. In this unit, we will extend the functionality of our calculateDiscount function by implementing five new requirements. Building on the previous unit, this course emphasizes practical experience by sequentially providing requirements through tests. Your mission is to implement code that satisfies each test, mirroring a real-world TDD scenario. Consider this guide your pair programmer, offering test-driven prompts to enhance your expertise incrementally.

Understanding the Red-Green-Refactor Cycle

As a reminder, the Red-Green-Refactor cycle is crucial in TDD, steering your development process: Red : Begin by writing a failing test to define what to do next. Green : Develop just enough code to pass the test, concentrating on meeting the functionality. Refactor : Enhance the code for clarity and efficiency without changing its behavior.

More Requirements for calculateDiscount Function

Below, you'll find additional requirements and tests designed to handle edge cases, such as negative discount percentages and capping maximum discounts. These enhancements aim to ensure the calculateDiscount function remains robust and reliable under various conditions.

6. Negative Discount Percentage

Description : The function should not accept negative discount percentages and must throw an error in such cases. Test Case : Kotlin import kotlin.test.Test import kotlin.test.assertFailsWith class DiscountCalculatorTest {@Test fun shouldThrowExceptionForDiscountsLessThanZeroPercent() {// Arrange val discountCalculator = DiscountCalculator() val originalPrice = 100.0 val discountPercentage = -10.0 // Act & Assert val exception = assertFailsWith<IllegalArgumentException> {discountCalculator.calculateDiscount(originalPrice, discountPercentage)} assert(exception.message == "Discount cannot be negative")}} This test ensures that the function throws an exception when a negative discount percentage is provided.

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Kotlin

import kotlin.test.Test
import kotlin.test.assertEquals

class DiscountCalculatorTest {
    @Test
    fun handleVerySmallPricesCorrectly() {
        // Arrange
        val discountCalculator = DiscountCalculator()
        val originalPrice = 0.001
        val discountPercentage = 1.0
        val expectedDiscountedPrice = 0.01 // Should not go below 0.01

        // Act
        val result = discountCalculator.calculateDiscount(originalPrice, discountPercentage)

        // Assert
        assertEquals(expectedDiscountedPrice, result, 0.001)
    }
}

import kotlin.test.Test
import kotlin.test.assertEquals

class DiscountCalculatorTest {
    @Test
    fun handleVerySmallPricesCorrectly() {
        // Arrange
        val discountCalculator = DiscountCalculator()
        val originalPrice = 0.001
        val discountPercentage = 1.0
        val expectedDiscountedPrice = 0.01 // Should not go below 0.01

        // Act
        val result = discountCalculator.calculateDiscount(originalPrice, discountPercentage)

        // Assert
        assertEquals(expectedDiscountedPrice, result, 0.001)
    }
}

Kotlin

import kotlin.test.Test
import kotlin.test.assertEquals

class DiscountCalculatorTest {
    @Test
    fun applyMinimumDiscountAmountWhenDiscountIsLessThanMinimum() {
        // Arrange
        val discountCalculator = DiscountCalculator()
        val originalPrice = 100.0
        val discountPercentage = 0.1 // 0.1% discount
        val expectedDiscountedPrice = 99.0 // Should apply minimum 1% discount

        // Act
        val result = discountCalculator.calculateDiscount(originalPrice, discountPercentage)

        // Assert
        assertEquals(expectedDiscountedPrice, result, 0.01)
    }
}

import kotlin.test.Test
import kotlin.test.assertEquals

class DiscountCalculatorTest {
    @Test
    fun applyMinimumDiscountAmountWhenDiscountIsLessThanMinimum() {
        // Arrange
        val discountCalculator = DiscountCalculator()
        val originalPrice = 100.0
        val discountPercentage = 0.1 // 0.1% discount
        val expectedDiscountedPrice = 99.0 // Should apply minimum 1% discount

        // Act
        val result = discountCalculator.calculateDiscount(originalPrice, discountPercentage)

        // Assert
        assertEquals(expectedDiscountedPrice, result, 0.01)
    }
}

Kotlin

import kotlin.test.Test
import kotlin.test.assertEquals

class DiscountCalculatorTest {
    @Test
    fun capMaximumDiscountAmountAt500() {
        // Arrange
        val discountCalculator = DiscountCalculator()
        val originalPrice = 2500.0
        val discountPercentage = 30.0 // Would normally be $750 off
        val expectedDiscountedPrice = 2000.0 // Should only apply $500 maximum discount

        // Act
        val result = discountCalculator.calculateDiscount(originalPrice, discountPercentage)

        // Assert
        assertEquals(expectedDiscountedPrice, result, 0.01)
    }
}

import kotlin.test.Test
import kotlin.test.assertEquals

class DiscountCalculatorTest {
    @Test
    fun capMaximumDiscountAmountAt500() {
        // Arrange
        val discountCalculator = DiscountCalculator()
        val originalPrice = 2500.0
        val discountPercentage = 30.0 // Would normally be $750 off
        val expectedDiscountedPrice = 2000.0 // Should only apply $500 maximum discount

        // Act
        val result = discountCalculator.calculateDiscount(originalPrice, discountPercentage)

        // Assert
        assertEquals(expectedDiscountedPrice, result, 0.01)
    }
}

Kotlin

import kotlin.test.Test
import kotlin.test.assertEquals

class DiscountCalculatorTest {
    @Test
    fun handleVerySmallPricesCorrectly() {
        // Arrange
        val discountCalculator = DiscountCalculator()
        val originalPrice = 0.001
        val discountPercentage = 1.0
        val expectedDiscountedPrice = 0.01 // Should not go below 0.01

        // Act
        val result = discountCalculator.calculateDiscount(originalPrice, discountPercentage)

        // Assert
        assertEquals(expectedDiscountedPrice, result, 0.001)
    }
}

Kotlin

import kotlin.test.Test
import kotlin.test.assertEquals

class DiscountCalculatorTest {
    @Test
    fun applyMinimumDiscountAmountWhenDiscountIsLessThanMinimum() {
        // Arrange
        val discountCalculator = DiscountCalculator()
        val originalPrice = 100.0
        val discountPercentage = 0.1 // 0.1% discount
        val expectedDiscountedPrice = 99.0 // Should apply minimum 1% discount

        // Act
        val result = discountCalculator.calculateDiscount(originalPrice, discountPercentage)

        // Assert
        assertEquals(expectedDiscountedPrice, result, 0.01)
    }
}

Kotlin

import kotlin.test.Test
import kotlin.test.assertEquals

class DiscountCalculatorTest {
    @Test
    fun capMaximumDiscountAmountAt500() {
        // Arrange
        val discountCalculator = DiscountCalculator()
        val originalPrice = 2500.0
        val discountPercentage = 30.0 // Would normally be $750 off
        val expectedDiscountedPrice = 2000.0 // Should only apply $500 maximum discount

        // Act
        val result = discountCalculator.calculateDiscount(originalPrice, discountPercentage)

        // Assert
        assertEquals(expectedDiscountedPrice, result, 0.01)
    }
}

Continue Developing the calculateDiscount Function

Understanding the Red-Green-Refactor Cycle

More Requirements for calculateDiscount Function

6. Negative Discount Percentage

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7. Handling Very Small Prices

8. Minimum Discount Percentage Application

9. Capping Maximum Discount Amount

Summary and Preparation for Practice