Fix wathced client test timing issue caused by late close (#13062)

There is a timing issue in the test, close may arrive late, or in
freeClientAsync we will free the client in async way, which will
lead to errors in watching_clients statistics, since we will only
unwatch all keys when we truly freeClient.

Add a wait here to avoid this problem. Also fixed some outdated
comments i saw. The test was introduced in #12966.

src/networking.c

@@ -1722,7 +1722,7 @@ void freeClient(client *c) {
     zfree(c);
 }
 
-/* Schedule a client to free it at a safe time in the serverCron() function.
+/* Schedule a client to free it at a safe time in the beforeSleep() function.
  * This function is useful when we need to terminate a client but we are in
  * a context where calling freeClient() is not possible, because the client
  * should be valid for the continuation of the flow of the program. */

tests/support/util.tcl

@@ -925,6 +925,14 @@ proc wait_for_blocked_clients_count {count {maxtries 100} {delay 10} {idx 0}} {
     }
 }
 
+proc wait_for_watched_clients_count {count {maxtries 100} {delay 10} {idx 0}} {
+    wait_for_condition $maxtries $delay  {
+        [s $idx watching_clients] == $count
+    } else {
+        fail "Timeout waiting for watched clients"
+    }
+}
+
 proc read_from_aof {fp} {
     # Input fp is a blocking binary file descriptor of an opened AOF file.
     if {[gets $fp count] == -1} return ""

tests/test_helper.tcl

@@ -284,7 +284,7 @@ proc redis_client {args} {
         set args [lrange $args 1 end]
     }
 
-    # create client that defers reading reply
+    # create client that won't defers reading reply
     set client [redis [srv $level "host"] [srv $level "port"] 0 $::tls]
 
     # select the right db and read the response (OK), or at least ping

tests/unit/info.tcl

@@ -458,9 +458,10 @@ start_server {tags {"info" "external:skip"}} {
             # unwatch without watch has no effect
             r unwatch
             assert_equal [s watching_clients] 1
-            # after disconnect
+            # after disconnect, since close may arrive later, or the client may
+            # be freed asynchronously, we use a wait_for_condition
             $r2 close
-            assert_equal [s watching_clients] 0
+            wait_for_watched_clients_count 0
         }
     }
 }