Update to Drupal 8.1.1. For more information, see https://www.drupal.org/node/2718713

core/tests/Drupal/FunctionalTests/Breadcrumb/Breadcrumb404Test.php

@@ -0,0 +1,57 @@
+<?php
+
+namespace Drupal\FunctionalTests\Breadcrumb;
+
+use Drupal\simpletest\BlockCreationTrait;
+use Drupal\Tests\BrowserTestBase;
+
+/**
+ * Tests the breadcrumb of 404 pages.
+ *
+ * @group breadcrumb
+ */
+class Breadcrumb404Test extends BrowserTestBase {
+
+  use BlockCreationTrait;
+
+  /**
+   * {@inheritdoc}
+   */
+  public static $modules = ['system', 'block'];
+
+  /**
+   * Tests that different 404s don't create unnecessary cache entries.
+   */
+  public function testBreadcrumbOn404Pages() {
+    $this->placeBlock('system_breadcrumb_block', ['id' => 'breadcrumb']);
+
+    // Prime the cache first.
+    $this->drupalGet('/not-found-1');
+    $base_count = count($this->getBreadcrumbCacheEntries());
+
+    $this->drupalGet('/not-found-2');
+    $next_count = count($this->getBreadcrumbCacheEntries());
+    $this->assertEquals($base_count, $next_count);
+
+    $this->drupalGet('/not-found-3');
+    $next_count = count($this->getBreadcrumbCacheEntries());
+    $this->assertEquals($base_count, $next_count);
+  }
+
+  /**
+   * Gets the breadcrumb cache entries.
+   *
+   * @return array
+   *   The breadcrumb cache entries.
+   */
+  protected function getBreadcrumbCacheEntries() {
+    $database = \Drupal::database();
+    $cache_entries = $database->select('cache_render')
+      ->fields('cache_render')
+      ->condition('cid', $database->escapeLike('entity_view:block:breadcrumb') . '%', 'LIKE')
+      ->execute()
+      ->fetchAllAssoc('cid');
+    return $cache_entries;
+  }
+
+}