Use in Espresso tests to wait for the idle state.

TestTools.kt

import android.support.test.InstrumentationRegistry
import java.util.concurrent.CountDownLatch

fun waitForIdle(errorMessage: String) {
    val countDownLatch = CountDownLatch(1)
    InstrumentationRegistry.getInstrumentation().waitForIdle { countDownLatch.countDown() }

    try {
        countDownLatch.await()
    } catch (e: InterruptedException) {
        throw RuntimeException(errorMessage, e)
    }
}