The logic from https://github.com/novoda/espresso-support bundled in a single .kt file

ViewTestRule.kt

import android.app.Activity
import android.app.Instrumentation
import android.content.Context
import android.support.annotation.LayoutRes
import android.support.test.InstrumentationRegistry
import android.support.test.rule.ActivityTestRule
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup

/**
 * Don't forget to add this Activity to your manifest.
 */

class ViewTestRuleActivity : Activity()

class ViewTestRule<T : View> constructor(
        private val instrumentation: Instrumentation,
        private val viewCreator: (Context, ViewGroup) -> T
) : ActivityTestRule<ViewTestRuleActivity>(ViewTestRuleActivity::class.java) {

    lateinit var view: T
        private set

    constructor(@LayoutRes resource: Int) : this(
            InstrumentationRegistry.getInstrumentation(),
            { context, parent ->
                LayoutInflater
                        .from(context)
                        .inflate(resource, parent, false)
                        .let { it as T }
            }
    )

    constructor(viewCreator: (Context, ViewGroup) -> T) : this(
            InstrumentationRegistry.getInstrumentation(),
            viewCreator
    )

    override fun afterActivityLaunched() {
        super.afterActivityLaunched()
        instrumentation.runOnMainSync {
            val root = activity
                    .findViewById<View>(android.R.id.content)
                    .let { it as ViewGroup }

            view = viewCreator(activity, root)
            activity.setContentView(view, view.layoutParams)
        }
    }

    fun runOnMainSynchronously(runner: (view: T) -> Unit) {
        instrumentation.runOnMainSync { runner(view) }
    }

}