diff -u b/core/modules/image/tests/src/Functional/ImageStyleDeleteTest.php b/core/modules/image/tests/src/Functional/ImageStyleDeleteTest.php
--- b/core/modules/image/tests/src/Functional/ImageStyleDeleteTest.php
+++ b/core/modules/image/tests/src/Functional/ImageStyleDeleteTest.php
@@ -77,8 +77,8 @@
     // Checks that the 'replacement' select element is displayed.
     $this->assertFieldByName('replacement');
     // Checks that UI messages are correct.
-    $this->assertRaw(t('If this style is in use on the site, you may select another style to replace it. All images that have been generated for this style will be permanently deleted. If no replacement style is selected, the dependent configurations might need manual reconfiguration.'));
-    $this->assertNoRaw(t('All images that have been generated for this style will be permanently deleted. The dependent configurations might need manual reconfiguration.'));
+    $this->assertSession()->responseContains(t('If this style is in use on the site, you may select another style to replace it. All images that have been generated for this style will be permanently deleted. If no replacement style is selected, the dependent configurations might need manual reconfiguration.'));
+    $this->assertSession()->responseNotContains(t('All images that have been generated for this style will be permanently deleted. The dependent configurations might need manual reconfiguration.'));
     // Delete 'wide' image style. Provide no replacement.
     $this->drupalPostForm(NULL, [], t('Delete'));