spek VS mockito-kotlin

Spek is a unit testing framework for Kotlin which supports Specification and Gherkin style.

The describe-it style is mainly used to write Spek tests. describe structure allows us to create a group of tests describing a specific method, and, in it, a specific scenario for the method is written. But it is also possible to use the GivenWhenThen style. Unfortunately, the framework doesn’t have embedded coroutine support, so we have to always use runBlockingTest { } for suspended functions. There is a ticket with this feature request on Github, but it seems it was never completed.

As you can see, I create mockUsersRepository object using mock( function. Then, in setup() method, I set up this repository in such a way so that it would return a list of hardcoded values. After this, on top of everything else, I check if, for mockUsersRepository object, getUsers method was called with verify function, in the test method. It’s important to note that Mockito is a very old framework and was originally written for Java. When Kotlin appeared, it turned out that out of the box this framework can work with some limitations, which is why an extension, mockito-kotlin, was released. The example above was written with it. Another Mockito’s limitation was that it was impossible to mock final classes and static methods, and all classes are final by default in Kotlin. Currently, this is solved through mockito-inline but, before, it was a serious limitation. In respect to Java development, there was and is an alternative for Android developers, PowerMock.

In the demo project, I used junit and mockito. One thing we need to pre-learn do the unit test, that is ksp class diagram.

What's wrong with Mockito for Kotlin?

Mockito does not work correctly with Kotlin types out of the box. Spring recommends using Mockk. There is also a special module for Mockito, which adds support for Kotlin - Mockito-Kotlin.