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

core/modules/block_content/tests/modules/block_content_test_views/test_views/views.view.test_block_content_view.yml

@@ -58,10 +58,10 @@ display:
             offset: false
             offset_label: Offset
           tags:
-            previous: '‹ previous'
-            next: 'next ›'
-            first: '« first'
-            last: 'last »'
+            previous: '‹ Previous'
+            next: 'Next ›'
+            first: '« First'
+            last: 'Last »'
           quantity: 9
       style:
         type: default

core/modules/block_content/tests/src/Unit/Plugin/migrate/source/d6/BoxTest.php

@@ -16,21 +16,15 @@ use Drupal\Tests\migrate\Unit\MigrateSqlSourceTestCase;
  */
 class BoxTest extends MigrateSqlSourceTestCase {
 
-  // The plugin system is not working during unit testing so the source plugin
-  // class needs to be manually specified.
   const PLUGIN_CLASS = 'Drupal\block_content\Plugin\migrate\source\d6\Box';
 
-  // The fake Migration configuration entity.
   protected $migrationConfiguration = array(
-    // The ID of the entity, can be any string.
     'id' => 'test',
     'source' => array(
       'plugin' => 'd6_boxes',
     ),
   );
 
-  // We need to set up the database contents; it's easier to do that below.
-  // These are sample result queries.
   protected $expectedResults = array(
     array(
       'bid' => 1,

core/modules/block_content/tests/src/Unit/Plugin/migrate/source/d7/BlockCustomTest.php

@@ -0,0 +1,45 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Tests\block_content\Unit\Plugin\migrate\source\d7\BlockCustomTest.
+ */
+
+namespace Drupal\Tests\block_content\Unit\Plugin\migrate\source\d7;
+
+use Drupal\block_content\Plugin\migrate\source\d7\BlockCustom;
+use Drupal\Tests\migrate\Unit\MigrateSqlSourceTestCase;
+
+/**
+ * @coversDefaultClass \Drupal\block_content\Plugin\migrate\source\d7\BlockCustom
+ * @group block_content
+ */
+class BlockCustomTest extends MigrateSqlSourceTestCase {
+
+  const PLUGIN_CLASS = BlockCustom::class;
+
+  protected $migrationConfiguration = array(
+    'id' => 'test',
+    'source' => array(
+      'plugin' => 'd7_block_custom',
+    ),
+  );
+
+  protected $expectedResults = array(
+    array(
+      'bid' => '1',
+      'body' => "I don't feel creative enough to write anything clever here.",
+      'info' => 'Meh',
+      'format' => 'filtered_html',
+    ),
+  );
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp() {
+    $this->databaseContents['block_custom'] = $this->expectedResults;
+    parent::setUp();
+  }
+
+}