val event = nextEvent() as Open
    return event.eventSource
  }

  fun assertClose() {
    nextEvent() as Closed
  }

  fun assertFailure(
    message: String?,
    code: Int? = null,
  ) {
    val event = nextEvent() as Failure
    if (code != null) {
      assertThat(event.response?.code).isEqualTo(code)
    }
    if (message != null) {
      assertThat(event.message).isEqualTo(message)