[ticket/11600] Increase code test coverage of avatar manager

Currently, not all methods and their possible behaviors are tested with unit tests.
Add them for better code coverage.

PHPBB3-11600
[ŧicket/11600] Split get driver tests into tests for all and only enabled ones

PHPBB3-11600
[ticket/11600] Use local variable for $user in test_localize_errors

PHPBB3-11600
[ticket/11600] Use lowercase null and remove duplicate test cases

PHPBB3-11600
Merge branch 'develop' of https://github.com/phpbb/phpbb3 into ticket/11600
[ticket/11600] Remove duplicate test case

PHPBB3-11600
[ticket/11553] Move bulletin points to pseudo class

Move bulletin points for .linklist lists to pseudo class
Group pseudo classes for .linklist.bulletin and .icon-notification

PHPBB3-11553
[ticket/11553] Replace bullet with unicode

PHPBB3-11553
[ticket/11553] Typo

PHPBB3-11553
[ticket/11686] Not checking for phpBB Debug errors on functional tests

PHPBB3-11686
Merge pull request #1473 from marc1706/ticket/11600

[ticket/11600] Increase code test coverage of avatar manager
[ticket/11690] Old module class names may get autoloaded by class_exists

PHPBB3-11690
Merge remote-tracking branch 'github-exreaction/ticket/11686' into develop-olympus

* github-exreaction/ticket/11686:
  [ticket/11686] Not checking for phpBB Debug errors on functional tests
Merge branch 'develop-olympus' into develop

* develop-olympus:
  [ticket/11686] Not checking for phpBB Debug errors on functional tests
Merge pull request #1553 from naderman/ticket/11690

[ticket/11690] Old module class names may get autoloaded by class_exists
Merge pull request #1429 from cyberalien/ticket/11553

Move bulletin points for linklist lists to pseudo classes
[ticket/11675] Fix template loop

PHPBB3-11675
Merge pull request #1554 from EXreaction/ticket/11675

[ticket/11675] Fix template loop
Merge branch 'develop' into feature/revisions

* develop:
  [ticket/11675] Fix template loop
  [ticket/11690] Old module class names may get autoloaded by class_exists
  [ticket/11686] Not checking for phpBB Debug errors on functional tests
  [ticket/11553] Typo
  [ticket/11553] Replace bullet with unicode
  [ticket/11553] Move bulletin points to pseudo class
  [ticket/11600] Remove duplicate test case
  [ticket/11600] Use lowercase null and remove duplicate test cases
  [ticket/11600] Use local variable for $user in test_localize_errors
  [ŧicket/11600] Split get driver tests into tests for all and only enabled ones
  [ticket/11600] Increase code test coverage of avatar manager