ConversationFilterTest uses a Tester class which calls beanManager.getContext(ConversationScoped.class).isActive();

The problem with the test is that this already might blow up with a BusyConversationException in OWB. But the test only expects the BCE a single line later.

From the spec:

The container ensures that a long-running conversation may be associated with at most one request at a time, by blocking or rejecting concurrent requests. If the container rejects a request, it must associate the request with a new transient conversation and throw an exception of type javax.enterprise.context.BusyConversationException.

We do this check already if you resolve the ConversationContext, which is perfectly allowed by the spec imo.