Currently, Gatling's WebSocket DSL expects you to define the number of expected messages: https://gatling.io/docs/gatling/reference/current/http/websocket/#set-a-check.

ws("Subscribe for updates")
  .sendText("")
  .await(10.seconds)(check1, ..., checkN)

In other words, you can create many checks with a method and a loop, but it has to be a finite loop with a fixed number of iterations.

A typical scenario for a websocket test is to subscribe to an infinite stream of updates on some event type (e.g. account update) and then perform checks on the received messages - something akin to

ws("Subscribe for updates")
  .sendText("")
  .during(10.seconds)(check) // keep consuming messages for 10 seconds, perform check

This is currently not possible.