Kotlin Unit testing - How to mock component of Companion object?

Question

If I have a (simplified) class that looks like this:

class MyManager @JvmOverloads constructor(/*constructor args*/) : MyManagerInterface {

    @Inject
    lateinit var myLogger: MyLogger

    init {
        component = DaggerLoggerComponent.builder()
                .loggerModule(LoggerModule(internalLogger))
                .build()

        component.inject(this)
    }

    companion object {
        lateinit var component: RemoteLoggerComponent
            private set
    }
}

When unit testing, how on earth do I mock the component in the companion object?

I've tried all kinds of tricks using Mockito, MockK etc but I come up against several obstacles.

The CUT (class-under-test) is another class that is using the MyManager component to inject its dependencies in its init block like so:

init {
        if(applicationContext == null) {
            throw IllegalStateException("Application Context must not be null")
        } else {

            MyManager.component.inject(this)
        }
    }

Basically, I'd be happy if the injection does nothing because I can set the dependencies externally for the sake of testing.

All help appreciated. Including if you think I'm coding this wrong. I'm relatively new to Kotlin and Dagger. Thanks.

score 42 · Accepted Answer · answered Aug 10 '18 at 22:17

42

Basically, using MockK, you need code like that:

mockkObject(MyManager)
every { MyManager.component.someOp(...) } returns 5

Not sure I understand all the details about the injection. As you said you can disable it.

answered Aug 10 '18 at 22:17

oleksiyp

2,659
19
15

1

My goodness! That seems to have worked. Thanks! I assumed that mockkObject was for mocking kotlin object declarations only. Obviously not. – the_new_mr Aug 13 '18 at 10:27
How about the using like this: `mockkObject(MyManager.Companion) every { MyManager.CompanionsomeOp(...) } returns 5 ` – Namo Sep 06 '21 at 09:58
2

Not working for me. – Kristy Welsh Oct 14 '21 at 17:48

score 2 · Answer 2 · answered May 07 '21 at 13:31

Do not forget to unmock companion objects. Otherwise, mocked version shall be used after the current test.

Blocked mocking shall unmock automatically for us:

mockkObject(MyManager) {
  every { MyManager.component.someOp(...) } returns 5

  act() 

  verify {
    ...
  }

}

Kotlin Unit testing - How to mock component of Companion object?

2 Answers2