Unit test Android custom view with AndroidX Test and Robolectric

setup_test_file.kt

package com.mobtiso.test.customview

import androidx.test.core.app.ApplicationProvider
import com.google.common.truth.Truth.assertThat
import org.junit.Test
import org.junit.runner.RunWith
import org.robolectric.RobolectricTestRunner
import org.robolectric.annotation.Config

@RunWith(RobolectricTestRunner::class)
@Config(sdk = [28])
class CountViewTest {

    private val context = ApplicationProvider.getApplicationContext<Context>();
    private val countView = CountView(context)
    private val buttonAdd = countView.findViewById<Button>(R.id.buttonAdd)
    private val textViewValue = countView.findViewById<TextView>(R.id.textView)

    @Test
    fun testSetUpIsOk() {
        assertThat(countView.context).isNotNull()
    }
}