fixed negative children_count after deleting categories

app/code/Magento/Catalog/Model/ResourceModel/Category/AggregateCount.php

@@ -8,11 +8,15 @@
 use Magento\Catalog\Model\Category;
 
 /**
+ * Aggregate count for parent category after deleting child category
+ *
  * Class AggregateCount
  */
 class AggregateCount
 {
     /**
+     * Reduces children count for parent categories
+     *
      * @param Category $category
      * @return void
      */
@@ -25,9 +29,7 @@ public function processDelete(Category $category)
          */
         $parentIds = $category->getParentIds();
         if ($parentIds) {
-            $childDecrease = $category->getChildrenCount() + 1;
-            // +1 is itself
-            $data = ['children_count' => new \Zend_Db_Expr('children_count - ' . $childDecrease)];
+            $data = ['children_count' => new \Zend_Db_Expr('children_count - 1')];
             $where = ['entity_id IN(?)' => $parentIds];
             $resourceModel->getConnection()->update($resourceModel->getEntityTable(), $data, $where);
         }

app/code/Magento/Catalog/Test/Unit/Model/ResourceModel/Category/AggregateCountTest.php

@@ -0,0 +1,91 @@
+<?php
+/**
+ * Copyright © Magento, Inc. All rights reserved.
+ * See COPYING.txt for license details.
+ */
+declare(strict_types=1);
+
+namespace Magento\Catalog\Test\Unit\Model\ResourceModel\Category;
+
+use Magento\Catalog\Model\Category;
+use Magento\Catalog\Model\ResourceModel\Category\AggregateCount;
+use Magento\Catalog\Model\ResourceModel\Category as ResourceCategory;
+use Magento\Framework\DB\Adapter\AdapterInterface;
+use Magento\Framework\TestFramework\Unit\Helper\ObjectManager as ObjectManagerHelper;
+use PHPUnit\Framework\MockObject\MockObject;
+use PHPUnit\Framework\TestCase;
+
+/**
+ * Aggregate count model test
+ */
+class AggregateCountTest extends TestCase
+{
+
+    /**
+     * @var AggregateCount
+     */
+    protected $aggregateCount;
+
+    /**
+     * @var ObjectManagerHelper
+     */
+    protected $objectManagerHelper;
+
+    /**
+     * @var Category|MockObject
+     */
+    protected $categoryMock;
+
+    /**
+     * @var  ResourceCategory|MockObject
+     */
+    protected $resourceCategoryMock;
+
+    /**
+     * @var AdapterInterface|MockObject
+     */
+    protected $connectionMock;
+
+    /**
+     * {@inheritdoc}
+     */
+    public function setUp(): void
+    {
+        $this->categoryMock = $this->createMock(Category::class);
+        $this->resourceCategoryMock = $this->createMock(ResourceCategory::class);
+        $this->connectionMock = $this->getMockBuilder(AdapterInterface::class)
+            ->getMockForAbstractClass();
+        $this->objectManagerHelper = new ObjectManagerHelper($this);
+        $this->aggregateCount = $this->objectManagerHelper->getObject(AggregateCount::class);
+    }
+
+    /**
+     * @return void
+     */
+    public function testProcessDelete(): void
+    {
+        $parentIds = 3;
+        $table = 'catalog_category_entity';
+
+        $this->categoryMock->expects($this->once())
+            ->method('getResource')
+            ->willReturn($this->resourceCategoryMock);
+        $this->categoryMock->expects($this->once())
+            ->method('getParentIds')
+            ->willReturn($parentIds);
+        $this->resourceCategoryMock->expects($this->any())
+            ->method('getEntityTable')
+            ->willReturn($table);
+        $this->resourceCategoryMock->expects($this->once())
+            ->method('getConnection')
+            ->willReturn($this->connectionMock);
+        $this->connectionMock->expects($this->once())
+            ->method('update')
+            ->with(
+                $table,
+                ['children_count' => new \Zend_Db_Expr('children_count - 1')],
+                ['entity_id IN(?)' => $parentIds]
+            );
+        $this->aggregateCount->processDelete($this->categoryMock);
+    }
+}

dev/tests/integration/testsuite/Magento/Catalog/Model/CategoryTest.php

@@ -49,7 +49,7 @@ class CategoryTest extends TestCase
      */
     protected $objectManager;
 
-    /** @var CategoryRepository */
+    /** @var CategoryResource */
     private $categoryResource;
 
     /** @var CategoryRepositoryInterface */
@@ -355,6 +355,17 @@ public function testDeleteChildren(): void
         $this->assertEquals($this->_model->getId(), null);
     }
 
+    /**
+     * @magentoDbIsolation enabled
+     * @magentoAppArea adminhtml
+     * @magentoDataFixture Magento/Catalog/_files/categories_no_products.php
+     */
+    public function testChildrenCountAfterDeleteParentCategory(): void
+    {
+        $this->categoryRepository->deleteByIdentifier(3);
+        $this->assertEquals(8, $this->categoryResource->getChildrenCount(1));
+    }
+
     /**
      * @magentoDataFixture Magento/Catalog/_files/category.php
      */