1. Follow this steps: https://antonioleiva.com/mockito-2-kotlin/

2. Update the libraries and replace androidTestImplementation with testImplementation. In my case:

   testImplementation "com.nhaarman.mockitokotlin2:mockito-kotlin:2.1.0 (update)

   testImplementation 'org.mockito:mockito-core:3.0.0' (update)

   testImplementation 'org.mockito:mockito-android:2.24.5' (replace androidTestImplementation with testImplementation)

3. Remove MockitoAnnotations.initMocks(this) from each Test class.

Tested with Android Studio 3.5

Mockito 2 now supports final classes and methods!

But for now that's an "incubating" feature. It requires some steps to activate it which are described in What's New in Mockito 2:

Mocking of final classes and methods is an incubating, opt-in feature. It uses a combination of Java agent instrumentation and subclassing in order to enable mockability of these types. As this works differently to our current mechanism and this one has different limitations and as we want to gather experience and user feedback, this feature had to be explicitly activated to be available ; it can be done via the mockito extension mechanism by creating the file src/test/resources/mockito-extensions/org.mockito.plugins.MockMaker containing a single line:

mock-maker-inline

After you created this file, Mockito will automatically use this new engine and one can do :

 final class FinalClass {
   final String finalMethod() { return "something"; }
 }

 FinalClass concrete = new FinalClass(); 

 FinalClass mock = mock(FinalClass.class);
 given(mock.finalMethod()).willReturn("not anymore");

 assertThat(mock.finalMethod()).isNotEqualTo(concrete.finalMethod());

In subsequent milestones, the team will bring a programmatic way of using this feature. We will identify and provide support for all unmockable scenarios. Stay tuned and please let us know what you think of this feature!

Since Mockito 2.1.0 there is a possibility to mock final types, enums, and final methods. It was already mentioned in the comments to the original question.

To do this, you’ll need to create a folder (if dont exist) test/resources/mockito-extensions and add there file with the name org.mockito.plugins.MockMaker and this line:

mock-maker-inline

Links to documentation and tutorial

This approach for mocking final classes unfortunately doesn't work for UI tests. For your UI tests, you'll have to work with the kotlin allopen plugin.