diff --git a/core/modules/field_ui/tests/src/Functional/FieldUiTestTrait.php b/core/modules/field_ui/tests/src/Functional/FieldUiTestTrait.php
new file mode 100644
index 0000000..c426add
--- /dev/null
+++ b/core/modules/field_ui/tests/src/Functional/FieldUiTestTrait.php
@@ -0,0 +1,127 @@
+<?php
+
+namespace Drupal\Tests\field_ui\Functional;
+
+/**
+ * Provides common functionality for the Field UI test classes.
+ */
+trait FieldUiTestTrait {
+
+  /**
+   * Creates a new field through the Field UI.
+   *
+   * @param string $bundle_path
+   *   Admin path of the bundle that the new field is to be attached to.
+   * @param string $field_name
+   *   The field name of the new field storage.
+   * @param string $label
+   *   (optional) The label of the new field. Defaults to a random string.
+   * @param string $field_type
+   *   (optional) The field type of the new field storage. Defaults to
+   *   'test_field'.
+   * @param array $storage_edit
+   *   (optional) $edit parameter for drupalPostForm() on the second step
+   *   ('Storage settings' form).
+   * @param array $field_edit
+   *   (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()) {
+    $label = $label ?: $this->randomString();
+    $initial_edit = array(
+      'new_storage_type' => $field_type,
+      'label' => $label,
+      'field_name' => $field_name,
+    );
+
+    // Allow the caller to set a NULL path in case they navigated to the right
+    // page before calling this method.
+    if ($bundle_path !== NULL) {
+      $bundle_path = "$bundle_path/fields/add-field";
+    }
+
+    // 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.');
+    // Test Breadcrumbs.
+    $this->assertLink($label, 0, 'Field label is correct in the breadcrumb of the storage settings page.');
+
+    // 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.');
+
+    // 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.');
+
+    // Check that the field appears in the overview form.
+    $this->assertSession()->elementExists('xpath', '//table[@id="field-overview"]//tr/td[1][text() = "' . $label . '"]');
+  }
+
+  /**
+   * Adds an existing field through the Field UI.
+   *
+   * @param string $bundle_path
+   *   Admin path of the bundle that the field is to be attached to.
+   * @param string $existing_storage_name
+   *   The name of the existing field storage for which we want to add a new
+   *   field.
+   * @param string $label
+   *   (optional) The label of the new field. Defaults to a random string.
+   * @param array $field_edit
+   *   (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()) {
+    $label = $label ?: $this->randomString();
+    $initial_edit = array(
+      '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'));
+    // 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('&amp;lt;', 'The page does not have double escaped HTML tags.');
+
+    // 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.');
+
+    // Check that the field appears in the overview form.
+    $this->assertSession()->elementExists('xpath', '//table[@id="field-overview"]//tr/td[1][text() = "' . $label . '"]');
+  }
+
+  /**
+   * Deletes a field through the Field UI.
+   *
+   * @param string $bundle_path
+   *   Admin path of the bundle that the field is to be deleted from.
+   * @param string $field_name
+   *   The name of the field.
+   * @param string $label
+   *   The label of the field.
+   * @param string $bundle_label
+   *   The label of the bundle.
+   */
+  public function fieldUIDeleteField($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.');
+
+    // Test Breadcrumbs.
+    $this->assertLink($label, 0, 'Field label is correct in the breadcrumb of the field delete page.');
+
+    // 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.');
+
+    // Check that the field does not appear in the overview form.
+    $this->assertSession()->elementNotExists('xpath', '//table[@id="field-overview"]//tr/td[1][text() = "' . $label . '"]');
+  }
+
+}
diff --git a/core/modules/link/tests/src/Functional/LinkFieldTest.php b/core/modules/link/tests/src/Functional/LinkFieldTest.php
index 3f07863..acad40c 100644
--- a/core/modules/link/tests/src/Functional/LinkFieldTest.php
+++ b/core/modules/link/tests/src/Functional/LinkFieldTest.php
@@ -475,9 +475,9 @@ function testLinkFormatter() {
                 $this->assertNotContains('<a href="' . Html::escape($url1) . '">' . Html::escape($url1) . '</a>', $output);
                 $this->assertNotContains('<a href="' . Html::escape($url2) . '">' . Html::escape($url2) . '</a>', $output);
                 $this->assertNotContains('<a href="' . Html::escape($url3) . '">' . Html::escape($url3) . '</a>', $output);
-                $this->assertContains(Html::escape($url1));
-                $this->assertContains(Html::escape($url2));
-                $this->assertContains(Html::escape($url3));
+                $this->assertContains(Html::escape($url1), $output);
+                $this->assertContains(Html::escape($url2), $output);
+                $this->assertContains(Html::escape($url3), $output);
               }
             }
             break;
@@ -630,7 +630,9 @@ protected function renderTestEntity($id, $view_mode = 'full', $reset = TRUE) {
     $entity = EntityTest::load($id);
     $display = entity_get_display($entity->getEntityTypeId(), $entity->bundle(), $view_mode);
     $content = $display->build($entity);
+
     $output = \Drupal::service('renderer')->renderRoot($content);
+    $output = (string) $output;
     $this->verbose($output);
     return $output;
   }
diff --git a/core/modules/link/tests/src/Functional/LinkFieldUITest.php b/core/modules/link/tests/src/Functional/LinkFieldUITest.php
index eeed78c..03c585c 100644
--- a/core/modules/link/tests/src/Functional/LinkFieldUITest.php
+++ b/core/modules/link/tests/src/Functional/LinkFieldUITest.php
@@ -3,7 +3,7 @@
 namespace Drupal\Tests\link\Functional;
 
 use Drupal\Component\Utility\Unicode;
-use Drupal\field_ui\Tests\FieldUiTestTrait;
+use Drupal\Tests\field_ui\Functional\FieldUiTestTrait;
 use Drupal\link\LinkItemInterface;
 use Drupal\Tests\BrowserTestBase;