versioning.truncate_privilege : GRANT fails with "Access denied", for root user

main.mysql_upgrade_noengine 'innodb'     [ pass ]   7889

versioning.truncate_privilege 'innodb'   [ fail ]

        Test ended at 2020-03-25 22:34:42

CURRENT_TEST: versioning.truncate_privilege

mysqltest: At line 37: query 'grant all on *.* to mysqltest_1@localhost' failed: 1045: Access denied for user 'root'@'localhost' (using password: NO)

The result from queries just before the failure was:

< snip >

connection root;

create table mysqltest.t (a int) with system versioning;