34 files declare their use of ImageStyle in Drupal 8

ConfigEntityImportTest.php in core/modules/system/tests/src/Kernel/Entity/ConfigEntityImportTest.php

FileMoveTest.php in core/modules/image/tests/src/Functional/FileMoveTest.php

image.module in core/modules/image/image.module

Exposes global functionality for creating image styles.

ImageAdminStylesTest.php in core/modules/image/tests/src/Functional/ImageAdminStylesTest.php

ImageAdminStylesTest.php in core/modules/image/tests/src/FunctionalJavascript/ImageAdminStylesTest.php

ImageDimensionsTest.php in core/modules/image/tests/src/Functional/ImageDimensionsTest.php

ImageEffectsTest.php in core/modules/image/tests/src/Functional/ImageEffectsTest.php

ImageFieldAttributesTest.php in core/modules/rdf/tests/src/Functional/ImageFieldAttributesTest.php

ImageFieldDisplayTest.php in core/modules/image/tests/src/Functional/ImageFieldDisplayTest.php

ImageFormatter.php in core/modules/image/src/Plugin/Field/FieldFormatter/ImageFormatter.php

ImageFormatterTest.php in core/modules/image/tests/src/Kernel/ImageFormatterTest.php

ImageImportTest.php in core/modules/image/tests/src/Kernel/ImageImportTest.php

ImageStyleCustomStreamWrappersTest.php in core/modules/image/tests/src/Kernel/ImageStyleCustomStreamWrappersTest.php

ImageStyleFlushTest.php in core/modules/image/tests/src/Functional/ImageStyleFlushTest.php

ImageStyleIntegrationTest.php in core/modules/image/tests/src/Kernel/ImageStyleIntegrationTest.php

ImageStyleResourceTestBase.php in core/modules/image/tests/src/Functional/Rest/ImageStyleResourceTestBase.php

ImageStylesPathAndUrlTest.php in core/modules/image/tests/src/Functional/ImageStylesPathAndUrlTest.php

ImageStyleTest.php in core/modules/jsonapi/tests/src/Functional/ImageStyleTest.php

ImageThemeFunctionTest.php in core/modules/image/tests/src/Kernel/ImageThemeFunctionTest.php

ImageWidget.php in core/modules/image/src/Plugin/Field/FieldWidget/ImageWidget.php

MediaLibraryAccessTest.php in core/modules/media_library/tests/src/Kernel/MediaLibraryAccessTest.php

MediaLibraryDisplayModeTest.php in core/modules/media_library/tests/src/Functional/MediaLibraryDisplayModeTest.php

MediaLibraryUpdateFormAndViewDisplaysTest.php in core/modules/media_library/tests/src/Functional/Update/MediaLibraryUpdateFormAndViewDisplaysTest.php

MediaSourceImageTest.php in core/modules/media/tests/src/FunctionalJavascript/MediaSourceImageTest.php

media_library.module in core/modules/media_library/media_library.module

Contains hook implementations for the media_library module.

media_library.post_update.php in core/modules/media_library/media_library.post_update.php

Post update functions for Media Library.

MigrateImageCacheTest.php in core/modules/image/tests/src/Kernel/Migrate/d6/MigrateImageCacheTest.php

MigrateImageStylesTest.php in core/modules/image/tests/src/Kernel/Migrate/d7/MigrateImageStylesTest.php

ResponsiveImageFieldDisplayTest.php in core/modules/responsive_image/tests/src/Functional/ResponsiveImageFieldDisplayTest.php

ResponsiveImageStyle.php in core/modules/responsive_image/src/Entity/ResponsiveImageStyle.php

responsive_image.module in core/modules/responsive_image/responsive_image.module

Responsive image display formatter for image fields.

StandardProfileTest.php in core/modules/rdf/tests/src/Functional/StandardProfileTest.php

UserPictureTest.php in core/modules/user/tests/src/Functional/UserPictureTest.php

ViewsConfigDependenciesIntegrationTest.php in core/modules/views/tests/src/Kernel/ViewsConfigDependenciesIntegrationTest.php