Mocking with MockK in Kotlin - Mini Project: Build & Apply

Mocking with MockK

📖 Scenario: You are writing tests for a simple calculator app. You want to check how your code behaves when the calculator service returns specific results without calling the real service.

🎯 Goal: Learn how to use MockK to create a mock of a calculator service, configure its behavior, and verify the output of a function that uses this service.

📋 What You'll Learn

Create an interface called CalculatorService with a function add(a: Int, b: Int): Int

Create a mock of CalculatorService using MockK

Configure the mock to return a specific value when add is called with certain arguments

Call the add function on the mock and print the result

💡 Why This Matters

🌍 Real World

Mocking helps you test your code without relying on real services or complex dependencies. This makes tests faster and more reliable.

💼 Career

Many software development jobs require writing unit tests. Knowing how to use mocking libraries like MockK is essential for testing Kotlin applications effectively.

1

Create the CalculatorService interface

Create an interface called CalculatorService with a function add(a: Int, b: Int): Int.

Kotlin

// Create interface CalculatorService with add function
// Your code here

Need a hint?

Use the interface keyword and define the add function with two Int parameters and an Int return type.

2

Create a mock of CalculatorService

Create a variable called mockCalculator and assign it a mock of CalculatorService using mockk().

Kotlin

interface CalculatorService {
    fun add(a: Int, b: Int): Int
}

// Create mockCalculator as a mock of CalculatorService
// Your code here

Need a hint?

Use val mockCalculator = mockk<CalculatorService>() to create the mock.

3

Configure the mock behavior

Use every { mockCalculator.add(2, 3) } to return 5.

Kotlin

import io.mockk.mockk
import io.mockk.every

interface CalculatorService {
    fun add(a: Int, b: Int): Int
}

val mockCalculator = mockk()

// Configure mockCalculator.add(2, 3) to return 5
// Your code here

Need a hint?

Use every { mockCalculator.add(2, 3) } returns 5 to set the mock's return value.

4

Call the mock and print the result

Call mockCalculator.add(2, 3) and print the result using println.

Kotlin

import io.mockk.mockk
import io.mockk.every

interface CalculatorService {
    fun add(a: Int, b: Int): Int
}

val mockCalculator = mockk()
every { mockCalculator.add(2, 3) } returns 5

// Call mockCalculator.add(2, 3) and print the result
// Your code here

Need a hint?

Call mockCalculator.add(2, 3), store it in result, then print result.