MAGETWO-71415 [The system grids] Mass actions process only 20 elements from all selected

- Add integration test for mass assign group for 21 customers
- Add 21 customers fixture
- Fix filter code style

Author: Michael Yu

app/code/Magento/Ui/Component/MassAction/Filter.php

@@ -223,15 +223,15 @@ private function getFilterIds($limit = true)
         if ($this->getDataProvider() instanceof \Magento\Ui\DataProvider\AbstractDataProvider) {
             // Use collection's getAllIds for optimization purposes.
             $idsArray = $this->getDataProvider()->getAllIds();
-        }else {
+        } else {
             $searchResult = $this->getDataProvider()->getSearchResult();
-            if($limit){
+            if ($limit) {
                 // Use compatible search api getItems when searchResult is not a collection.
                 foreach ($searchResult->getItems() as $item) {
                     /** @var $item \Magento\Framework\Api\Search\DocumentInterface */
                     $idsArray[] = $item->getId();
                 }
-            }else{
+            } else {
                 //Grab all selected even if they are not on the current page.
                 $idsArray = $searchResult->getAllIds();
             }

dev/tests/integration/testsuite/Magento/Customer/Controller/Adminhtml/Index/MassAssignGroupTest.php

@@ -69,6 +69,33 @@ public function testMassAssignGroupAction()
         $this->assertEquals(0, $customer->getGroupId());
     }
 
+    /**
+     * @magentoDataFixture Magento/Customer/_files/twenty_one_customers.php
+     */
+    public function testLargeGroupMassAssignGroupAction()
+    {
+
+        for($i = 1; $i < 22; $i++){
+            $customer = $this->customerRepository->getById($i);
+            $this->assertEquals(1, $customer->getGroupId());
+        }
+
+        $this->getRequest()
+            ->setParam('group', 0)
+            ->setPostValue('namespace', 'customer_listing')
+            ->setPostValue('selected', [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21]);
+        $this->dispatch('backend/customer/index/massAssignGroup');
+        $this->assertSessionMessages(
+            $this->equalTo(['A total of 21 record(s) were updated.']),
+            \Magento\Framework\Message\MessageInterface::TYPE_SUCCESS
+        );
+        $this->assertRedirect($this->stringStartsWith($this->baseControllerUrl));
+        for($i = 1; $i < 22; $i++){
+            $customer = $this->customerRepository->getById($i);
+            $this->assertEquals(0, $customer->getGroupId());
+        }
+    }
+
     /**
      * Valid group Id but no customer Ids specified
      * @magentoDbIsolation enabled