override fun writeTo(sink: BufferedSink) {
    requestBodySinks.add(sink)
  }

  override fun isDuplex(): Boolean = true

  @Throws(InterruptedException::class)
  fun takeSink(): BufferedSink {
    return requestBodySinks.poll(5, SECONDS) ?: throw AssertionError("no sink to take")
  }

  fun assertNoMoreSinks() {
    assertTrue(requestBodySinks.isEmpty())
  }

          body = requestBody,
        ),
      )

    call.execute().use { response ->
      assertThat(response.body.string()).isEqualTo("abc")
      val requestBodyOut = requestBody.takeSink()
      assertFailsWith<IOException> {
        SlowRequestBody.writeTo(requestBodyOut)
      }
      assertFailsWith<IOException> {
        requestBodyOut.close()
      }
    }