If the system is under high load 'show full processlist' might report the

process of the predecessing test case instead of the current test case. 
Shifting the command to the end of the current test case should avoid this problem. 

mysql-test/r/ps_grant.result

-prepare stmt4 from ' show full processlist ';
-execute stmt4;
-Id	User	Host	db	Command	Time	State	Info
-number	root	localhost	test	Query	time	NULL	show full processlist
 test_sequence
 ------ grant/revoke/drop affects a parallel session test ------
 show grants for second_user@localhost ;
@@ -79,3 +75,7 @@ commit ;
 show grants for second_user@localhost ;
 ERROR 42000: There is no such grant defined for user 'second_user' on host 'localhost'
 drop database mysqltest;
+prepare stmt4 from ' show full processlist ';
+execute stmt4;
+Id	User	Host	db	Command	Time	State	Info
+number	root	localhost	test	Query	time	NULL	show full processlist

mysql-test/t/ps_grant.test

 # Can't test grants with embedded server
 -- source include/not_embedded.inc
 
-# Tested here simply so it is not tested with embedded server
-prepare stmt4 from ' show full processlist ';
---replace_column 1 number 6 time 3 localhost
-execute stmt4;
 
 let $type= 'MYISAM' ;
 
@@ -116,4 +112,9 @@ show grants for second_user@localhost ;
 
 drop database mysqltest;
 
+# Tested here simply so it is not tested with embedded server
+prepare stmt4 from ' show full processlist ';
+--replace_column 1 number 6 time 3 localhost
+execute stmt4;
+