* It also confirms we enforce the 250 ms delay in each race.
   */
  @Test
  fun tcpConnectionsRaceAfterTlsFails() {
    val plan0 = routePlanner.addPlan()
    plan0.tcpConnectDelayNanos = 280.ms

    val plan1 = routePlanner.addPlan()
    plan1.tcpConnectDelayNanos = 10.ms // Connect at time = 260 ms.
    plan1.tlsConnectDelayNanos = 10.ms // Connect at time = 270 ms.
    plan1.tlsConnectThrowable = IOException("boom!")

feature OkHttp will attempt both IPv6 and IPv4 connections concurrently, keeping whichever connects
first. Fast fallback gives IPv6 connections a 250 ms head start so IPv6 is preferred on networks
where it's available.

To opt-in, configure your `OkHttpClient.Builder`:


```
OkHttpClient client = new OkHttpClient.Builder()
    .fastFallback(true)