6 files declare their use of YamlDefinitionsLoader in Hook Event Dispatcher 3.x

EntityEventTest.php in modules/preprocess_event_dispatcher/tests/src/Unit/EntityEventTest.php

EntityEventVariablesTest.php in modules/preprocess_event_dispatcher/tests/src/Unit/EntityEventVariablesTest.php

FactoryMapperTest.php in modules/preprocess_event_dispatcher/tests/src/Unit/FactoryMapperTest.php

OtherEventTest.php in modules/preprocess_event_dispatcher/tests/src/Unit/OtherEventTest.php

OtherEventVariablesTest.php in modules/preprocess_event_dispatcher/tests/src/Unit/OtherEventVariablesTest.php

PreprocessEventPassTest.php in modules/preprocess_event_dispatcher/tests/src/Unit/PreprocessEventPassTest.php