MAGETWO-35656: \Magento\Framework\Stdlib\DateTime\DateTime methods malformed

Author: AndriyNasinnyk

lib/internal/Magento/Framework/Stdlib/DateTime/DateTime.php

@@ -114,7 +114,7 @@ public function gmtTimestamp($input = null)
             return false;
         }
         $date = $this->_localeDate->date($result);
-        $timestamp = $date->getTimestamp() - $date->getTimezone()->getOffset($date);
+        $timestamp = $date->getTimestamp();
         unset($date);
         return $timestamp;
     }

lib/internal/Magento/Framework/Stdlib/Test/Unit/DateTime/DateTimeTest.php

@@ -0,0 +1,32 @@
+<?php
+/**
+ * Copyright © 2015 Magento. All rights reserved.
+ * See COPYING.txt for license details.
+ */
+namespace Magento\Framework\Stdlib\Test\Unit\DateTime;
+
+use \Magento\Framework\Stdlib\DateTime\DateTime;
+
+/**
+ * Magento\Framework\Stdlib\DateTimeTest test case
+ */
+class DateTimeTest extends \PHPUnit_Framework_TestCase
+{
+    /**
+     * @test
+     */
+    public function testGmtTimestamp()
+    {
+        $timezone = $this->getMockBuilder('Magento\Framework\Stdlib\DateTime\TimezoneInterface')->getMock();
+        $timezone->expects($this->any())
+            ->method('date')
+            ->willReturn(new \DateTime('2015-04-02 21:03:00'));
+        /** @var \Magento\Framework\Stdlib\DateTime\TimezoneInterface $timezone */
+
+        $dateTime = new DateTime($timezone);
+        $this->assertEquals(
+            gmdate('U', strtotime('2015-04-02 21:03:00')),
+            $dateTime->gmtTimestamp('2015-04-02 21:03:00')
+        );
+    }
+}