diff --git a/core/modules/field_ui/tests/src/Functional/FieldUiTestTrait.php b/core/modules/field_ui/tests/src/Functional/FieldUiTestTrait.php
index c426add..1ff2be7 100644
--- a/core/modules/field_ui/tests/src/Functional/FieldUiTestTrait.php
+++ b/core/modules/field_ui/tests/src/Functional/FieldUiTestTrait.php
@@ -2,6 +2,8 @@
 
 namespace Drupal\Tests\field_ui\Functional;
 
+use Drupal\Component\Render\FormattableMarkup;
+
 /**
  * Provides common functionality for the Field UI test classes.
  */
@@ -26,13 +28,13 @@
    *   (optional) $edit parameter for drupalPostForm() on the third step ('Field
    *   settings' form).
    */
-  public function fieldUIAddNewField($bundle_path, $field_name, $label = NULL, $field_type = 'test_field', array $storage_edit = array(), array $field_edit = array()) {
+  protected function fieldUIAddNewField($bundle_path, $field_name, $label = NULL, $field_type = 'test_field', array $storage_edit = [], array $field_edit = []) {
     $label = $label ?: $this->randomString();
-    $initial_edit = array(
+    $initial_edit = [
       'new_storage_type' => $field_type,
       'label' => $label,
       'field_name' => $field_name,
-    );
+    ];
 
     // Allow the caller to set a NULL path in case they navigated to the right
     // page before calling this method.
@@ -41,18 +43,18 @@ public function fieldUIAddNewField($bundle_path, $field_name, $label = NULL, $fi
     }
 
     // First step: 'Add field' page.
-    $this->drupalPostForm($bundle_path, $initial_edit, t('Save and continue'));
-    $this->assertRaw(t('These settings apply to the %label field everywhere it is used.', array('%label' => $label)), 'Storage settings page was displayed.');
+    $this->drupalPostForm($bundle_path, $initial_edit, 'Save and continue');
+    $this->assertSession()->responseContains(new FormattableMarkup('These settings apply to the %label field everywhere it is used.', ['%label' => $label]));
     // Test Breadcrumbs.
-    $this->assertLink($label, 0, 'Field label is correct in the breadcrumb of the storage settings page.');
+    $this->assertSession()->linkExists($label);
 
     // Second step: 'Storage settings' form.
-    $this->drupalPostForm(NULL, $storage_edit, t('Save field settings'));
-    $this->assertRaw(t('Updated field %label field settings.', array('%label' => $label)), 'Redirected to field settings page.');
+    $this->drupalPostForm(NULL, $storage_edit, 'Save field settings');
+    $this->assertSession()->responseContains(new FormattableMarkup('Updated field %label field settings.', ['%label' => $label]));
 
     // Third step: 'Field settings' form.
-    $this->drupalPostForm(NULL, $field_edit, t('Save settings'));
-    $this->assertRaw(t('Saved %label configuration.', array('%label' => $label)), 'Redirected to "Manage fields" page.');
+    $this->drupalPostForm(NULL, $field_edit, 'Save settings');
+    $this->assertSession()->responseContains(new FormattableMarkup('Saved %label configuration.', ['%label' => $label]));
 
     // Check that the field appears in the overview form.
     $this->assertSession()->elementExists('xpath', '//table[@id="field-overview"]//tr/td[1][text() = "' . $label . '"]');
@@ -72,25 +74,25 @@ public function fieldUIAddNewField($bundle_path, $field_name, $label = NULL, $fi
    *   (optional) $edit parameter for drupalPostForm() on the second step
    *   ('Field settings' form).
    */
-  public function fieldUIAddExistingField($bundle_path, $existing_storage_name, $label = NULL, array $field_edit = array()) {
+  protected function fieldUIAddExistingField($bundle_path, $existing_storage_name, $label = NULL, array $field_edit = []) {
     $label = $label ?: $this->randomString();
-    $initial_edit = array(
+    $initial_edit = [
       'existing_storage_name' => $existing_storage_name,
       'existing_storage_label' => $label,
-    );
+    ];
 
     // First step: 'Re-use existing field' on the 'Add field' page.
-    $this->drupalPostForm("$bundle_path/fields/add-field", $initial_edit, t('Save and continue'));
+    $this->drupalPostForm("$bundle_path/fields/add-field", $initial_edit, 'Save and continue');
     // Set the main content to only the content region because the label can
     // contain HTML which will be auto-escaped by Twig.
     $main_content = $this->cssSelect('.region-content');
     $this->setRawContent(reset($main_content)->asXml());
-    $this->assertRaw('field-config-edit-form', 'The field config edit form is present.');
-    $this->assertNoRaw('<', 'The page does not have double escaped HTML tags.');
+    $this->assertSession()->responseContains('field-config-edit-form');
+    $this->assertSession()->responseNotContains('<');
 
     // Second step: 'Field settings' form.
-    $this->drupalPostForm(NULL, $field_edit, t('Save settings'));
-    $this->assertRaw(t('Saved %label configuration.', array('%label' => $label)), 'Redirected to "Manage fields" page.');
+    $this->drupalPostForm(NULL, $field_edit, 'Save settings');
+    $this->assertSession()->responseContains(new FormattableMarkup('Saved %label configuration.', ['%label' => $label]));
 
     // Check that the field appears in the overview form.
     $this->assertSession()->elementExists('xpath', '//table[@id="field-overview"]//tr/td[1][text() = "' . $label . '"]');
@@ -108,17 +110,17 @@ public function fieldUIAddExistingField($bundle_path, $existing_storage_name, $l
    * @param string $bundle_label
    *   The label of the bundle.
    */
-  public function fieldUIDeleteField($bundle_path, $field_name, $label, $bundle_label) {
+  protected function fieldUIDeleteField($bundle_path, $field_name, $label, $bundle_label) {
     // Display confirmation form.
     $this->drupalGet("$bundle_path/fields/$field_name/delete");
-    $this->assertRaw(t('Are you sure you want to delete the field %label', array('%label' => $label)), 'Delete confirmation was found.');
+    $this->assertSession()->responseContains(new FormattableMarkup('Are you sure you want to delete the field %label', ['%label' => $label]));
 
     // Test Breadcrumbs.
-    $this->assertLink($label, 0, 'Field label is correct in the breadcrumb of the field delete page.');
+    $this->assertSession()->linkExists($label);
 
     // Submit confirmation form.
-    $this->drupalPostForm(NULL, array(), t('Delete'));
-    $this->assertRaw(t('The field %label has been deleted from the %type content type.', array('%label' => $label, '%type' => $bundle_label)), 'Delete message was found.');
+    $this->drupalPostForm(NULL, [], 'Delete');
+    $this->assertSession()->responseContains(new FormattableMarkup('The field %label has been deleted from the %type content type.', ['%label' => $label, '%type' => $bundle_label]));
 
     // Check that the field does not appear in the overview form.
     $this->assertSession()->elementNotExists('xpath', '//table[@id="field-overview"]//tr/td[1][text() = "' . $label . '"]');