Intro to TDD with Kotlin and JUnit

Welcome to your first lesson in this course dedicated to practicing Test-Driven Development (TDD) using Kotlin and JUnit. Test-Driven Development is an effective approach that emphasizes writing tests before coding. This methodology helps you design your application with testing as a core element, ensuring each component behaves as expected. In this lesson, you'll learn the fundamentals of TDD along with the Red-Green-Refactor cycle, understanding their roles in creating robust and maintainable code.

This course involves hands-on practice, where you'll receive requirements through tests incrementally. Your task is to implement code that makes each test pass, mirroring a real-world TDD environment. Consider this course guide as your pair programmer, providing you with test-driven prompts to enhance your skills as you advance.

As a reminder, the Red-Green-Refactor cycle is central to TDD, guiding your development process:

• Red: Start by writing a failing test to define the next step.
• Green: Implement just enough code to pass the test, focusing on functionality.
• Refactor: Optimize the code for clarity and efficiency without changing its behavior.

Below, you’ll find the detailed requirements and corresponding test cases for the calculateDiscount function.

Each requirement focuses on a specific behavior the function must fulfill, guiding you through the TDD process step by step.

• Description: The function must correctly apply a percentage-based discount to an original price.
• Test Case:
  Kotlin

  import kotlin.test.Test
  import kotlin.test.assertEquals
  
  class DiscountCalculatorTest {
  
      @Test
      fun testCalculateDiscountAppliesCorrectDiscount() {
          // Arrange
          val discountCalculator = DiscountCalculator()
          val originalPrice = 100.0
          val discountPercentage = 20.0
          val expectedDiscountedPrice = 80.0
  
          // Act
          val result = discountCalculator.calculateDiscount(originalPrice, discountPercentage)
  
          // Assert
          assertEquals(expectedDiscountedPrice, result, 0.01)
      }
  }

  The test ensures that the function applies the discount correctly and tolerates minor floating-point deviations.