Application.class mock in Android UnitTest

I have an Application class.

open class AppController : MultiDexApplication() {

    companion object {

        @JvmStatic
        lateinit var instance: AppController
            private set

    }

    override fun onCreate() {
        super.onCreate()

        instance = this
    }

}

I use my code for extension.
Int.kt

fun Int.pxToDp(): Int {
    return TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_PX, this.toFloat(), AppControllerMaster.instance.applicationContext.resources.displayMetrics).toInt()
}

I need to use that in a unit test.
when use that I get this error

kotlin.UninitializedPropertyAccessException: lateinit property instance has not been initialized

I need to create a mock or alternative AppController.class in my unit test.

I need to use it in UnitTest, not androidTest.

how can Application Crete or mock in UNITTEST?

Refer http://robolectric.org/

Robolectric is a framework that brings fast and reliable unit tests to Android.
Tests run inside the JVM on your workstation in seconds

I found an answer without using Robolectric.

I create a function extension in package com.example in class with the name ContextEX.kt

ContextEX.kt

fun Any.getContextEX(): Context {
    return AppController.instance
}

and change pxToDp extention.

change AppControllerMaster.instance.applicationContext to getContextEX().

fun Int.pxToDp(): Int {
    return TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_PX, this.toFloat(), getContextEX().resources.displayMetrics).toInt()
}

and in the test, I mock Application class and context extension with Mockk library

val context: Context = spyk()

// Mock Context extension
mockkStatic("com.example.ContextEXKt") // notic: not ContextEX.kt

val metrics: DisplayMetrics = mockk()
val resources: Resources = mockk()

every {
   any<Any>().getContext()
}.answers {
   context
}

every {
   any<Any>().getContext().resources
}.answers {
   resources
}

every {
   any<Any>().getContext().resources.displayMetrics
}.answers {
   metrics
}