Issue #2505997 by olli, peterpoe, Lendude: User error: "preview" is an invalid render array key

core/modules/views/tests/modules/views_test_config/test_views/views.view.test_preview_error.yml

+langcode: en
+status: true
+dependencies:
+  module:
+    - user
+id: test_preview_error
+label: test_preview_error
+module: views
+description: ''
+tag: ''
+base_table: views_test_data
+base_field: id
+core: 8.x
+display:
+  default:
+    display_plugin: default
+    id: default
+    display_title: Master
+    position: null
+    display_options:
+      row:
+        type: fields
+      fields: { }

core/modules/views_ui/src/Tests/PreviewTest.php

@@ -21,7 +21,7 @@ class PreviewTest extends UITestBase {
    *
    * @var array
    */
-  public static $testViews = array('test_preview', 'test_pager_full', 'test_mini_pager');
+  public static $testViews = array('test_preview', 'test_preview_error', 'test_pager_full', 'test_mini_pager');
 
   /**
    * Tests contextual links in the preview form.
@@ -230,6 +230,18 @@ public function testPreviewAdditionalInfo() {
     $this->assertRaw('css/views_ui_test.test.css', 'Attached CSS asset found.');
   }
 
+  /**
+   * Tests view validation error messages in the preview.
+   */
+  public function testPreviewError() {
+    $this->drupalGet('admin/structure/views/view/test_preview_error/edit');
+    $this->assertResponse(200);
+
+    $this->drupalPostForm(NULL, $edit = array(), t('Update preview'));
+
+    $this->assertText('Unable to preview due to validation errors.', 'Preview error text found.');
+  }
+
   /**
    * Get the preview form and force an AJAX preview update.
    *

core/modules/views_ui/src/ViewUI.php

@@ -818,7 +818,7 @@ public function renderPreview($display_id, $args = array()) {
           drupal_set_message($error, 'error');
         }
       }
-      $preview = t('Unable to preview due to validation errors.');
+      $preview = ['#markup' => t('Unable to preview due to validation errors.')];
     }
 
     // Assemble the preview, the query info, and the query statistics in the