NOTE: Use PHP 5.4+ during this test
Preparations:
# don't apply patch yet
# open the {nav Tools > System Tools} section in Admin Console in one tab
# open homepage in other tab and confirm, that no error happens
# create an empty trait (in separate file) in the `/core/units/users/` folder
# register trait in `RegisterClasses` array in `users_config.php` (don't rebuild any caches yet)
# use trait in the `UsersEventHandler` class
# reload tab with homepage and confirm, that now Fatal Error (related to missing trait) is shown in debugger
Actual test:
# press `Deploy` button in {nav Tools > System Tools} section in Admin Console and confirm, that now Fatal Error (related to missing trait) is shown in debugger
# run `do_update` script on In-Portal folder and confirm that it ends up with same Fatal Error
# apply patch
# run `do_update` script and confirm, that no error happens and homepage can be opened after that
# rewind the test to get fatal error again
# press `Deploy` button in {nav Tools > System Tools} section in Admin Console and confirm, that no error happens and homepage can be opened after that