Mocking extension function in Kotlin

Question

How to mock Kotlin extension function using Mockito or PowerMock in tests? Since they are resolved statically should they be tested as static method calls or as non static?

Answer 1

First of all, Mockito knows nothing Kotlin specific language constructs. In the end, Mockito will have a look into the byte code. Mockito is only able to understand what it finds there and what looks like a Java language construct.

Meaning: to be really sure, you might want to use javap to deassemble the compiled classfiles to identify the exact names/signatures of the methods you want to mock.

And obviously: when that method is static, you have to user PowerMock, or JMockit; if not, you should prefer to with Mockito.

From a java point of view, you simply avoid mocking static stuff; but of course, things get really interesting, now that different languages with different ideas/concepts come together.