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

vendor/phpunit/phpunit-mock-objects/tests/_fixture/PartialMockTestClass.php

@@ -0,0 +1,18 @@
+<?php
+class PartialMockTestClass
+{
+    public $constructorCalled = false;
+
+    public function __construct()
+    {
+        $this->constructorCalled = true;
+    }
+
+    public function doSomething()
+    {
+    }
+
+    public function doAnotherThing()
+    {
+    }
+}