Is it possible to use Mockito with Kotlin without open the class?

Question

As we probably know, by default Kotlin class once defined, it is final, unless it is explicitly declared open.

This would post a challenge when we want to Mock it using Mockito. We need to explicitly declare it as open. Is there a way we could avoid declaring it as open while able to Mock it for our testing?

Answer 1

The MockMaker plugin doesn't seem to work when running espresso tests. Therefore, you can use Kotlin's all-open pugin instead.

Add the plugin in build.gradle:

buildscript {
    dependencies {
        classpath "org.jetbrains.kotlin:kotlin-allopen:$kotlin_version"
    }
}

apply plugin: "kotlin-allopen"

Specify the annotation that will make the class open:

allOpen {
    annotation("com.my.MyMockable")
}

Create your annotation which can be used to annotate classes:

@Target(AnnotationTarget.CLASS)
annotation class MyMockable

Then, in order to make your class and its public methods Mockable (open), annotate it with your annotation:

@MyMockable

Answer 2

Mockito2 can now mock final classes as well.

However, this feature is opt-in, so you need to enable it manually.
To do so, you need to define a file /mockito-extensions/org.mockito.plugins.MockMaker containing the line mock-maker-inline

See e.g.
http://hadihariri.com/2016/10/04/Mocking-Kotlin-With-Mockito/ or https://github.com/mockito/mockito/wiki/What%27s-new-in-Mockito-2#unmockable
for a quick introduction

on a side note, this currently doesn't work for android