Bug #18495: mysqltest does not use the correct error number

  When looking up the error number for named errors in mysqltest .test
  files, we inadvertantly would match ER_WRONG_VALUE against
  ER_WRONG_VALUE_COUNT because we were using the length of the shorter
  string in strncmp(). Now we double-check the length of matches to
  make sure it was a complete match.

client/mysqltest.c

@@ -1956,7 +1956,13 @@ static uint get_errcodes(match_err *to,struct st_query *q)
 	;
       for (; e->name; e++)
       {
-	if (!strncmp(start, e->name, (int) (p - start)))
+        /*
+          If we get a match, we need to check the length of the name we
+          matched against in case it was longer than what we are checking
+          (as in ER_WRONG_VALUE vs. ER_WRONG_VALUE_COUNT).
+        */
+	if (!strncmp(start, e->name, (int) (p - start)) &&
+            strlen(e->name) == (p - start))
 	{
 	  to[count].code.errnum= (uint) e->code;
 	  to[count].type= ERR_ERRNO;

mysql-test/t/events.test

@@ -320,9 +320,9 @@ drop event one_event;
 create event e_26 on schedule at '2017-01-01 00:00:00' disable do set @a = 5;
 select db, name, body, definer, convert_tz(execute_at, 'UTC', 'SYSTEM'), on_completion from mysql.event;
 drop event e_26;
---error 1504
+--error ER_WRONG_VALUE
 create event e_26 on schedule at NULL disabled do set @a = 5;
---error 1504
+--error ER_WRONG_VALUE
 create event e_26 on schedule at 'definitely not a datetime' disabled do set @a = 5;
 
 set names utf8;