Junit test for suscription mapping not working

I have been referring to this https://docs.spring.io/spring-graphql/docs/current/reference/html/#testing to setup test for the subscriptionMapping
However when I run the test the subscription start but does not emit the message and ends up in a hangup state.
Can someone help me in what am I missing

@SpringBootTest(webEnvironment = SpringBootTest.WebEnvironment.DEFINED_PORT)
class SubscriptionControllerTest {
    val client: WebSocketClient = ReactorNettyWebSocketClient()
    val tester = WebSocketGraphQlTester.builder(url, client)
    .build()
    


    @Test
    
    fun createTestSubscription() {
        
        val responseFlux: Flux = tester.document(
        "subscription ($var1: String, $var2: String) {n" +
        " testSubscription(var1: $var1, var2: $var2) {n" +
        " valuen" +
        "}"
        ).variable("var1", var1).variable("var2", var2)
        .executeSubscription()
        .toFlux("testSubscription",DTO::class.java)

            subscriptionService.publish(sampleData)

            StepVerifier
                .create(responseFlux)
                 .expectSubscription()
                .expectNext(sampleData)
                .verifyComplete()
        }
}