Update to Drupal 8.1.2. For more information, see https://www.drupal.org/project/drupal/releases/8.1.2

core/lib/Drupal/Core/Test/HttpClientMiddleware/TestHttpClientMiddleware.php

@@ -40,7 +40,7 @@ class TestHttpClientMiddleware {
                   // Call \Drupal\simpletest\WebTestBase::error() with the parameters from
                   // the header.
                   $parameters = unserialize(urldecode($header_value));
-                  if (count($parameters) === 3)  {
+                  if (count($parameters) === 3) {
                     throw new \Exception($parameters[1] . ': ' . $parameters[0] . "\n" . Error::formatBacktrace([$parameters[2]]));
                   }
                   else {

core/lib/Drupal/Core/Test/TestDatabase.php

@@ -0,0 +1,44 @@
+<?php
+
+namespace Drupal\Core\Test;
+
+use Drupal\Core\Database\ConnectionNotDefinedException;
+use Drupal\Core\Database\Database;
+
+/**
+ * Provides helper methods for interacting with the Simpletest database.
+ */
+class TestDatabase {
+
+  /**
+   * Returns the database connection to the site running Simpletest.
+   *
+   * @return \Drupal\Core\Database\Connection
+   *   The database connection to use for inserting assertions.
+   *
+   * @see \Drupal\simpletest\TestBase::prepareEnvironment()
+   */
+  public static function getConnection() {
+    // Check whether there is a test runner connection.
+    // @see run-tests.sh
+    // @todo Convert Simpletest UI runner to create + use this connection, too.
+    try {
+      $connection = Database::getConnection('default', 'test-runner');
+    }
+    catch (ConnectionNotDefinedException $e) {
+      // Check whether there is a backup of the original default connection.
+      // @see TestBase::prepareEnvironment()
+      try {
+        $connection = Database::getConnection('default', 'simpletest_original_default');
+      }
+      catch (ConnectionNotDefinedException $e) {
+        // If TestBase::prepareEnvironment() or TestBase::restoreEnvironment()
+        // failed, the test-specific database connection does not exist
+        // yet/anymore, so fall back to the default of the (UI) test runner.
+        $connection = Database::getConnection('default', 'default');
+      }
+    }
+    return $connection;
+  }
+
+}