MAGETWO-35064: At night (by Kiev time) some tests connected to dates are failed

app/code/Magento/Checkout/Test/Unit/Helper/DataTest.php

@@ -123,8 +123,9 @@ class DataTest extends \PHPUnit_Framework_TestCase
             );
 
         $this->_checkoutSession = $arguments['checkoutSession'];
-        $localeDate = $arguments['localeDate'];
-        $localeDate->expects($this->any())->method('date')->will($this->returnValue('Oct 02, 2013'));
+        $arguments['localeDate']->expects($this->any())
+            ->method('formatDateTime')
+            ->willReturn('Oct 02, 2013');
 
         $this->_transportBuilder = $arguments['transportBuilder'];
 

app/code/Magento/Customer/Test/Unit/Controller/Account/EditPostTest.php

@@ -252,13 +252,13 @@ class EditPostTest extends \PHPUnit_Framework_TestCase
         $this->customerAccountManagement
             ->expects($this->once())
             ->method('changePassword')
-            ->willThrowException(new \Magento\Framework\Exception\AuthenticationException('Error'));
+            ->willThrowException(new \Magento\Framework\Exception\AuthenticationException(__('Error')));
         $this->messageManager
             ->expects($this->once())
             ->method('addError')
             ->with('Error');
 
-        $exception = new \Magento\Framework\Exception\InputException('Error');
+        $exception = new \Magento\Framework\Exception\InputException(__('Error'));
         $this->customerRepository
             ->expects($this->once())
             ->method('save')

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

@@ -233,7 +233,7 @@ class Timezone implements TimezoneInterface
      * @param null $locale
      * @param null $timezone
      * @param string|null $pattern
-     * @return mixed
+     * @return string
      */
     public function formatDateTime(
         \DateTimeInterface $date,

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

@@ -122,7 +122,7 @@ interface TimezoneInterface
      * @param null $locale
      * @param null $timezone
      * @param string|null $pattern
-     * @return mixed
+     * @return string
      */
     public function formatDateTime(
         \DateTimeInterface $date,