WebSocket testing - can't capture incoming messages

I'm trying to test WebSockets in SpringBoot application, however it is not working. Subscriber that should capture incoming message is not doing it.

@Configuration
@EnableWebSocketMessageBroker
internal class WsConfig : WebSocketMessageBrokerConfigurer {

    override fun configureMessageBroker(config: MessageBrokerRegistry) {
        config.enableSimpleBroker("/queue")
        config.setApplicationDestinationPrefixes("/app")
    }

    override fun registerStompEndpoints(registry: StompEndpointRegistry) {
        registry.addEndpoint("/ws").withSockJS()
    }
}

@Controller
class WsController(private val messagingTemplate: SimpMessagingTemplate) {

    @MessageMapping("/chat")
    fun sendChatMessage(@Payload message: String) = messagingTemplate.convertAndSend("/queue/chat", message)
}

And the test itself.

@SpringBootTest(webEnvironment = SpringBootTest.WebEnvironment.RANDOM_PORT)
class WsTest(@LocalServerPort private val port: Int) {

    private val wsClient = createWebSocketClient()
    private val lock = CountDownLatch(1)

    @Test
    fun test1() {
        val subscriber = connect()
        val publisher = connect()
        val capturedMessages = mutableListOf<String>()

        subscriber.subscribe("/queue/chat", frameHandler(capturedMessages))
        publisher.send("/app/chat", "lorem ipsum")

        lock.await(5, TimeUnit.SECONDS)
        Assertions.assertEquals(1, capturedMessages.size)
    }


    private fun createWebSocketClient(): WebSocketStompClient {
        val webSocketClient = WebSocketStompClient(SockJsClient(listOf(WebSocketTransport(StandardWebSocketClient()))))
        webSocketClient.messageConverter = MappingJackson2MessageConverter()
        return webSocketClient
    }

    private fun connect() = wsClient.connect("ws://localhost:$port/ws", object : StompSessionHandlerAdapter() {}).get(2, TimeUnit.SECONDS)

    private fun frameHandler(messages: MutableList<String>) =
            object : StompSessionHandlerAdapter() {
                override fun getPayloadType(headers: StompHeaders): Type {
                    return String::class.java
                }

                override fun handleFrame(headers: StompHeaders, payload: Any?) {
                    messages.add(payload as String)
                }
            }
}

Long story short, handleFrame() is not beeing called at all and I'm out of ideas why is that happening.