.../QuickEditIntegrationTest.php                   | 67 +++++++++++++++++++++-
 1 file changed, 64 insertions(+), 3 deletions(-)

diff --git a/core/modules/quickedit/tests/src/FunctionalJavaScript/QuickEditIntegrationTest.php b/core/modules/quickedit/tests/src/FunctionalJavaScript/QuickEditIntegrationTest.php
index a990f02..9841503 100644
--- a/core/modules/quickedit/tests/src/FunctionalJavaScript/QuickEditIntegrationTest.php
+++ b/core/modules/quickedit/tests/src/FunctionalJavaScript/QuickEditIntegrationTest.php
@@ -2,11 +2,12 @@
 
 namespace Drupal\Tests\quickedit\FunctionalJavascript;
 
+use Drupal\block_content\Entity\BlockContent;
+use Drupal\block_content\Entity\BlockContentType;
 use Drupal\Core\Field\FieldStorageDefinitionInterface;
 use Drupal\editor\Entity\Editor;
 use Drupal\field\Tests\EntityReference\EntityReferenceTestTrait;
 use Drupal\filter\Entity\FilterFormat;
-use Drupal\FunctionalJavascriptTests\JavascriptTestBase;
 use Drupal\taxonomy\Entity\Term;
 use Drupal\taxonomy\Entity\Vocabulary;
 
@@ -20,7 +21,7 @@ class QuickEditIntegrationTest extends QuickEditJavaScriptTestBase {
   /**
    * {@inheritdoc}
    */
-  public static $modules = ['node', 'editor', 'ckeditor', 'taxonomy'];
+  public static $modules = ['node', 'editor', 'ckeditor', 'taxonomy', 'block', 'block_content'];
 
   /**
    * A user with permissions to edit Articles and use Quick Edit.
@@ -82,6 +83,9 @@ protected function setUp() {
       ->setComponent($field_name, ['type' => 'entity_reference_label'])
       ->save();
 
+    $this->drupalPlaceBlock('page_title_block');
+    $this->drupalPlaceBlock('system_main_block');
+
     // Log in as a content author who can use Quick Edit and edit Articles.
     $this->contentAuthorUser = $this->drupalCreateUser([
       'access contextual links',
@@ -92,6 +96,7 @@ protected function setUp() {
       'edit any article content',
       'use text format some_format',
       'edit terms in tags',
+      'administer blocks',
     ]);
     $this->drupalLogin($this->contentAuthorUser);
   }
@@ -250,6 +255,62 @@ public function testArticleNode() {
     ]);
   }
 
-  // @todo test custom block
+  /**
+   * Tests if a custom can be in-place edited with Quick Edit.
+   */
+  public function testCustomBlock() {
+    $block_content_type = BlockContentType::create(array(
+      'id' => 'basic',
+      'label' => 'basic',
+      'revision' => FALSE
+    ));
+    $block_content_type->save();
+    block_content_add_body_field($block_content_type->id());
+
+    $block_content = BlockContent::create([
+      'info' => 'Llama',
+      'type' => 'basic',
+      'body' => [
+        'value' => 'The name "llama" was adopted by European settlers from native Peruvians.',
+        'format' => 'some_format',
+      ],
+    ]);
+    $block_content->save();
+    $this->drupalPlaceBlock('block_content:' . $block_content->uuid(), [
+      'label' => 'My custom block!',
+    ]);
+
+    $this->drupalGet('');
+
+    // Initial state.
+    $this->awaitQuickEditForEntity('block_content', 1);
+    $this->assertEntityInstanceStates([
+      'block_content/1[0]' => 'closed',
+    ]);
+
+    // Start in-place editing of the article node.
+    $this->startQuickEditViaToolbar('block_content', 1, 0);
+    $this->assertEntityInstanceStates([
+      'block_content/1[0]' => 'opened',
+    ]);
+    $this->assertQuickEditEntityToolbar((string) $block_content->label(), NULL);
+    $this->assertEntityInstanceFieldStates('block_content', 1, 0, [
+      'block_content/1/body/en/full' => 'candidate',
+    ]);
+
+    // Click the body field.
+    $this->click('[data-quickedit-entity-id="block_content/1"] .field--name-body');
+    $this->assertQuickEditEntityToolbar((string) $block_content->label(), 'Body');
+    $this->assertEntityInstanceFieldStates('block_content', 1, 0, [
+      'block_content/1/body/en/full' => 'active',
+    ]);
+
+    // Wait for CKEditor to load, then verify it has.
+    $this->assertJsCondition('CKEDITOR.status === "loaded"');
+    $this->assertEntityInstanceFieldMarkup('block_content', 1, 0, [
+      'block_content/1/body/en/full' => '.cke_editable_inline',
+    ]);
+    $this->assertSession()->elementExists('css', '#quickedit-entity-toolbar .quickedit-toolgroup.wysiwyg-main > .cke_chrome .cke_top[role="presentation"] .cke_toolbar[role="toolbar"] .cke_toolgroup[role="presentation"] > .cke_button[title="Bold"][role="button"]');
+  }
 
 }