Mockito vs mockk: What are the differences?

Introduction

In this article, we will be discussing the key differences between Mockito and MockK, two popular mocking frameworks used in Java and Kotlin respectively.

1. Compatibility and Language Support: Mockito is primarily used for mocking in Java projects, whereas MockK is specifically designed for mocking in Kotlin projects. Mockito supports both Java and Kotlin, but it may not have as native support for certain Kotlin-specific features compared to MockK.

2. Syntax and API: Mockito uses a more traditional syntax and API with static methods and method chaining. On the other hand, MockK provides a more concise and expressive syntax using Kotlin's DSL (Domain-Specific Language) capabilities, which makes it easier to write and read mocking code.

3. Nullability Handling: Mockito does not differentiate between nullable and non-nullable types, which means it does not enforce null safety in its API. MockK, being a Kotlin-specific framework, is designed with null safety in mind and provides better support for handling nullable types, allowing developers to avoid potential null pointer exceptions.

4. Coroutines Support: MockK has built-in support for mocking coroutines, which is a key advantage for Kotlin developers. It provides functions and methods specifically designed to handle coroutine-related scenarios, such as suspending functions and delay operations. Mockito, being a Java-centric framework, does not have out-of-the-box support for mocking coroutines.

5. Spying vs Mocking: In Mockito, both mocking and spying (partial mocking) are supported. Spying allows you to partially mock an object while still calling the real methods on it. MockK, on the other hand, only supports mocking and does not have built-in support for spying. If you need to perform partial mocking in MockK, you would generally need to resort to other Kotlin-specific techniques.

6. Verification: Mockito provides various assertion methods for verifying method invocations, such as verify, verifyZeroInteractions, and verifyNoMoreInteractions. MockK also provides similar verification capabilities but with a slightly different syntax using the verify function. MockK's syntax is more concise and follows the Kotlin conventions.

In summary, Mockito is a popular mocking framework for Java that can also be used in Kotlin, whereas MockK is a mocking framework specifically designed for Kotlin. MockK provides a more Kotlin-native syntax, better null safety handling, and built-in support for mocking coroutines, while Mockito offers greater flexibility with spying and a syntax more familiar to Java developers.