Unit test on Kotlin Extension Function on Android SDK Classes

Kotlin extension function is great. But how could I perform unit test on them? Especially those that is of Android SDK provided class (e.g. Context, Dialog).

I provide two examples below, and if anyone could share how I could unit test them, or if I need to write them differently if I really want to unit test them.

fun Context.getColorById(colorId: Int): Int {
    if (Build.VERSION.SDK_INT >= 23)
        return ContextCompat.getColor(this, colorId)
    else return resources.getColor(colorId)
}

and

fun Dialog.setupErrorDialog(body : String, onOkFunc: () -> Unit = {}): Dialog {
    window.requestFeature(Window.FEATURE_NO_TITLE)
    this.setContentView(R.layout.dialog_error_layout)

    (findViewById(R.id.txt_body) as TextView).text = body
    (findViewById(R.id.txt_header) as TextView).text = context.getString(R.string.dialog_title_error)
    (findViewById(R.id.txt_okay)).setOnClickListener{
        onOkFunc()
        dismiss()
    }
    return this
}

Any suggestion would help. Thanks!