@Throws(UnknownHostException::class)
  override fun lookup(hostname: String): List<InetAddress> {
    requestedHosts.add(hostname)
    return hostAddresses[hostname] ?: throw UnknownHostException()
  }

  fun assertRequests(vararg expectedHosts: String?) {
    assertThat(requestedHosts).containsExactly(*expectedHosts)
    requestedHosts.clear()
  }

  /** Allocates and returns `count` fake IPv4 addresses like [255.0.0.100, 255.0.0.101].  */