val request = server.takeRequest()
    assertThat(request.requestLine).isEqualTo("POST /foo HTTP/1.1")
    assertArrayEquals(postBytes, request.body.readByteArray())
    assertThat(request.headers["Content-Length"]!!.toInt()).isEqualTo(postBytes.size)
  }

  @ParameterizedTest
  @ArgumentsSource(ProtocolParamProvider::class)
  fun closeAfterFlush(
    protocol: Protocol,
    mockWebServer: MockWebServer,
  ) {

      checkNotNull(certificateChainCleaner) { "certificateChainCleaner == null" }
      checkNotNull(x509TrustManager) { "x509TrustManager == null" }
    }
  }

  /** Prepares the [request] to be executed at some point in the future. */
  override fun newCall(request: Request): Call = RealCall(this, request, forWebSocket = false)

  /** Uses [request] to connect a new web socket. */
  override fun newWebSocket(
    request: Request,