Architecture-components-samples: How does OpenForTesting annotation work?

[amrro]

In GithubBrowserSample,

Mockito cannot mock final classes and Kotlin class is final by defualt. But @yigit solved it by using OpenForTesting annotation.

I found that OpenForTesting annotation exists in both Release and debug sources. I've tried to find out how it works, but I couldn't.

Could someone explain how this annotation works, or how does it make Kotlin classes open for Mockito?

[amrro]

This explains everything.