MAGETWO-84822: Mock ObjectManager for each test to keep from failing when run individually but not as part of suite

Author: pdohogne-magento

dev/tests/unit/phpunit.xml.dist

@@ -38,6 +38,9 @@
             </exclude>
         </whitelist>
     </filter>
+    <listeners>
+        <listener class="Magento\Framework\TestFramework\Unit\Listener\ReplaceObjectManager"/>
+    </listeners>
     <logging>
         <!--coverage_html_placeholder
             <log type="coverage-html" target="{{coverage_dir}}/test-reports/coverage" charset="UTF-8" yui="true" highlight="true"/>

lib/internal/Magento/Framework/TestFramework/Unit/Listener/ReplaceObjectManager.php

@@ -0,0 +1,42 @@
+<?php
+/**
+ * Copyright © 2013-2017 Magento, Inc. All rights reserved.
+ * See COPYING.txt for license details.
+ */
+namespace Magento\Framework\TestFramework\Unit\Listener;
+
+use Magento\Framework\App\ObjectManager;
+use Magento\Framework\ObjectManagerInterface;
+
+/**
+ * The event listener which instantiates ObjectManager before test run
+ */
+class ReplaceObjectManager extends \PHPUnit_Framework_BaseTestListener
+{
+    /**
+     * Replaces ObjectManager before run for each test
+     *
+     * Replace existing instance of the Application's ObjectManager with the mock.
+     *
+     * This avoids the issue with a not initialized ObjectManager
+     * and makes working with ObjectManager predictable as it always contains clear mock for each test
+     *
+     * @param \PHPUnit_Framework_Test $test
+     * @return void
+     */
+    public function startTest(\PHPUnit_Framework_Test $test)
+    {
+        if ($test instanceof \PHPUnit_Framework_TestCase) {
+            $objectManagerMock = $test->getMockBuilder(ObjectManagerInterface::class)
+                ->getMockForAbstractClass();
+            $createMockCallback = function ($type) use ($test) {
+                return $test->getMockBuilder($type)
+                    ->disableOriginalConstructor()
+                    ->getMockForAbstractClass();
+            };
+            $objectManagerMock->method('create')->willReturnCallback($createMockCallback);
+            $objectManagerMock->method('get')->willReturnCallback($createMockCallback);
+            ObjectManager::setInstance($objectManagerMock);
+        }
+    }
+}