MQE-580: [Unit Test] CestObjectHandler.php

- add new test for getCestsByGroup function
- extract mock logic into new function

Author: imeron2433

dev/tests/unit/Magento/FunctionalTestFramework/Test/Handlers/CestObjectHandlerTest.php

@@ -188,7 +188,6 @@ public function testGetCestsByGroup()
         $coh = CestObjectHandler::getInstance();
         $cests = $coh->getCestsByGroup('test');
 
-
         // perform asserts
         $this->assertCount(2, $cests);
         $this->assertArrayHasKey($this->testCestName . '2', $cests);