Issue #1785770 by dawehner: Improve the handler base test.

lib/Drupal/views/Plugin/views/HandlerBase.php

lib/Drupal/views/Tests/Handler/HandlerTest.php

...t_config/config/views.view.test_handler_relationships.yml

..._test_data/config/views.view.test_handler_test_access.yml

...b/Drupal/views_test_data/Plugin/views/field/FieldTest.php

tests/views_test_data/views_test_data.module

views_ui/admin.inc