Useful testing code from Udacity's Android Kotlin Developer Nanodegree.

AppNavigationTest.kt

/**
 * Extension function to obtain the content description for the navigation icon.
 */
fun <T : Activity> ActivityScenario<T>.getToolbarNavigationContentDescription(): String {
    var description = ""
    onActivity {
        description =
            it.findViewById<Toolbar>(R.id.toolbar).navigationContentDescription as String
    }
    return description
}

EspressoIdlingResource.kt

/**
 * Useful function to test long running operations without adding too much boilerplate.
 */
inline fun <T> wrapEspressoIdlingResource(function: () -> T): T {
    // Espresso does not work well with coroutines yet. See
    // https://github.com/Kotlin/kotlinx.coroutines/issues/982
    EspressoIdlingResource.increment() // Set app as busy.
    return try {
        function()
    } finally {
        EspressoIdlingResource.decrement() // Set app as idle.
    }
}