LateinitSample.kt

import com.google.inject.Guice
import javax.inject.Inject
import kotlin.properties.Delegates

class Greeter {
  fun greet() {
    println("Hello")
  }
}

class Client {

  @Inject
  lateinit val greeter1: Greeter

  @Inject
  val greeter2: Greeter by Delegates.notNull()
}

fun main(args: Array<String>) {
  val injector = Guice.createInjector()
  val client = injector.getInstance(Client::class.java)
  client.greeter1.greet() //=> Hello
  client.greeter2.greet() // IllegalStateException thrown
}

LateinitSample2.kt

import org.junit.Before
import org.junit.Test
import org.mockito.Mockito.mock
import kotlin.properties.Delegates

interface Greeter {
  fun greet()
}

class Client {
  lateinit var greeter1: Greeter
  var greeter2: Greeter by Delegates.notNull()
}

class ClientTest {

  val sut = Client()

  @Before
  fun setUp() {
    sut.greeter1 = mock(Greeter::class.java)
    sut.greeter2 = mock(Greeter::class.java)
  }

  @Test
  fun test() {
    sut.greeter1.greet()
    sut.greeter2.greet()
  }
}