val startNanos = System.nanoTime()
    sink.write(Buffer().writeUtf8("f"), 1)
    assertFailsWith<InterruptedIOException> {
      sink.flush() // This will time out waiting on the write window.
    }
    val elapsedNanos = System.nanoTime() - startNanos
    awaitWatchdogIdle()
    // 200ms delta
    assertThat(TimeUnit.NANOSECONDS.toMillis(elapsedNanos).toDouble())