OnClearTestDemo.kt

import androidx.lifecycle.ViewModel
import androidx.lifecycle.ViewModelProvider
import androidx.lifecycle.ViewModelStore
import androidx.lifecycle.ViewModelStoreOwner
import org.amshove.kluent.shouldBe
import org.junit.Test

class MyViewModel : ViewModel() {
    var isCleared = false

    override fun onCleared() {
        isCleared = true
    }
}

class ViewModelHolder(val subjectViewModel: ViewModel) : ViewModelStoreOwner {
    private val viewModelStore = ViewModelStore()

    init {
        val provider = ViewModelProvider(this, object: ViewModelProvider.Factory {
            override fun <T : ViewModel?> create(modelClass: Class<T>): T = subjectViewModel as T
        })
        // Put the subjectViewModel into the store.
        provider.get(ViewModel::class.java)
    }

    override fun getViewModelStore(): ViewModelStore = viewModelStore

    fun performClear() {
        viewModelStore.clear()
    }
}

class OnClearedViewModelTest {

    @Test
    fun onCleared() {
        val myViewModelProvider =  MyViewModel()

        myViewModelProvider.isCleared shouldBe false

        ViewModelHolder(myViewModelProvider).performClear()

        myViewModelProvider.isCleared shouldBe true
    }
}