Update to drupal 8.0.0-rc1. For more information, see https://www.drupal.org/node/2582663

core/modules/block/src/Tests/BlockTest.php

@@ -135,6 +135,9 @@ class BlockTest extends BlockTestBase {
    * Test configuring and moving a module-define block to specific regions.
    */
   function testBlock() {
+    // Place page title block to test error messages.
+    $this->drupalPlaceBlock('page_title_block');
+
     // Select the 'Powered by Drupal' block to be configured and moved.
     $block = array();
     $block['id'] = 'system_powered_by_block';