https://pekko.apache.org/japi/pekko-http/snapshot/org/apache/pekko/http/impl/engine/ws/MessageSpec.ClientTestSetup.html
MessageSpec.ClientTestSetup
declaration: package: org.apache.pekko.http.impl.engine.ws, class: MessageSpec, class: ClientTestSetup
https://pekko.apache.org/japi/pekko-http/current/org/apache/pekko/http/impl/engine/ws/MessageSpec.ServerTestSetup.html
MessageSpec.ServerTestSetup