Do not let the asking's Close shut the stand-in's connection before its cleanup (issue 604)

The asking helper registered a.Close, which closes the shared test connection; the stand-in's cleanup ran after it on a closed connection, so its consumer was never deleted and blocked the next test on the workqueue stream.

internal/link/asking_nats_test.go

@@ -39,7 +39,13 @@ func asking(t *testing.T, conn *nats.Conn, js nats.JetStreamContext, node string
 		t.Fatal(err)
 	}
 	a := &natsAsking{conn: conn, js: js, inbox: inbox, answers: answers, lost: make(chan error, 1)}
-	t.Cleanup(a.Close)
+	// **Not a.Close.** Close closes the connection, and this connection is the test's own, shared with
+	// the stand-in. Cleanups run last-in first-out and the stand-in was made first, so its cleanup
+	// would run on a closed connection: Unsubscribe returns ErrConnectionClosed without deleting the
+	// consumer it made, and every request after that fails. The consumer then outlives the test on a
+	// workqueue stream, which allows one consumer per filter, and the next test cannot subscribe
+	// (issue 604). The connection is closed by aBus, last of all.
+	t.Cleanup(func() { _ = answers.Unsubscribe() })
 	return a
 }
 
@@ -109,9 +115,13 @@ func standinGone(t *testing.T, js nats.JetStreamContext, stream, durable string)
 	t.Helper()
 	deadline := time.Now().Add(5 * time.Second)
 	for {
-		if _, err := js.ConsumerInfo(stream, durable); errors.Is(err, nats.ErrConsumerNotFound) {
+		_, err := js.ConsumerInfo(stream, durable)
+		if errors.Is(err, nats.ErrConsumerNotFound) {
 			return
 		}
+		if errors.Is(err, nats.ErrConnectionClosed) {
+			t.Fatalf("the connection closed before consumer %s was deleted: %v", durable, err)
+		}
 		_ = js.DeleteConsumer(stream, durable)
 		if time.Now().After(deadline) {
 			t.Fatalf("consumer %s on %s still exists 5s after it was deleted", durable, stream)