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Mastering Test-Driven Development (TDD) with Kotlin — Building a Todo List Manager

Introduction:

Test-Driven Development (TDD) is a powerful software development approach that ensures code reliability and maintainability by writing tests before implementing the actual code. In this blog, we’ll explore the principles of TDD through a hands-on example of building a Todo List Manager application using Kotlin.

Principle 1: Write a Failing Test (Red) 🔴

Let’s begin by writing a failing test to implement the addition of a task to our Todo List Manager:

import org.junit.Test
import org.junit.Assert.assertEquals
class TodoListManagerTest {
    @Test
    fun testAddTask() {
        val todoListManager = TodoListManager()
        todoListManager.addTask("Buy groceries")
        assertEquals(1, todoListManager.getTotalTasks())
    }
}

In this test, we create an instance of our `TodoListManager` class and call the addTask method to add a task. Since we haven’t implemented the TodoListManager class yet, this test will fail (Red).

Principle 2: Write the Simplest Code to Pass the Test (Green) 🟢

With a failing test, let’s move on to the next step. We’ll implement the TodoListManager class to make the test pass (Green).

class TodoListManager {
    private val tasks = mutableListOf<String>()
    
    fun addTask(task: String) {
        tasks.add(task)
    }
    
    fun getTotalTasks(): Int {
        return tasks.size
    }
}

With this straightforward implementation, our test now passes, indicating that the task addition functionality works correctly (Green).

Principle 3: Refactor the Code (Refactor) 🟡

Next, let’s refactor the TodoListManager class for better maintainability:

class TodoListManager {
    private val tasks = mutableListOf<String>()
    
    fun addTask(task: String) {
        tasks.add(task)
    }
    
    fun getTotalTasks(): Int = tasks.size
}

The test ensures that our refactoring hasn’t affected the correctness of the TodoListManager class.

Principle 4: Write Additional Tests and Iteratively Improve

Now that our basic task addition functionality is working, let’s expand the capabilities of our Todo List Manager with more tests.

@Test
fun testCompleteTask() {
    val todoListManager = TodoListManager()
    
    todoListManager.addTask("Buy groceries")
    todoListManager.addTask("Finish report")
    todoListManager.completeTask("Buy groceries")
    
    assertEquals(1, todoListManager.getRemainingTasks())
}
@Test
fun testClearTasks() {
    val todoListManager = TodoListManager()
    
    todoListManager.addTask("Buy groceries")
    todoListManager.addTask("Finish report")
    todoListManager.clearTasks()
    
    assertEquals(0, todoListManager.getTotalTasks())
}

By iteratively adding more functionality to the TodoListManager class, we create corresponding tests, ensuring that each test fails before writing the implementation.

Advantages of TDD:

1. Early Detection of Bugs: TDD helps catch and fix bugs early in the development process, reducing the risk of defects in the final code.

2. Better Code Design: By focusing on test cases, TDD encourages modular and well-structured code design.

3. Confident Refactoring: Automated tests act as a safety net, providing confidence when refactoring or making changes to the codebase.

Conclusion:

Test-Driven Development is a valuable practice that leads to higher code quality and maintainability. By writing tests first and iteratively building functionality, developers can create software that is more reliable, easier to maintain, and better suited to handle future changes.

In this blog, we explored the principles of TDD through a practical example of building a Todo List Manager application with Kotlin. Embrace TDD as part of your development process, and it will guide you towards becoming a more confident and efficient developer.

Happy coding! 🚀