diff --git a/tests/unit/Espo/ORM/CollectionTest.php b/tests/unit/Espo/ORM/CollectionTest.php
new file mode 100644
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+++ b/tests/unit/Espo/ORM/CollectionTest.php
@@ -0,0 +1,120 @@
+<?php
+/************************************************************************
+ * This file is part of EspoCRM.
+ *
+ * EspoCRM - Open Source CRM application.
+ * Copyright (C) 2014-2023 Yurii Kuznietsov, Taras Machyshyn, Oleksii Avramenko
+ * Website: https://www.espocrm.com
+ *
+ * EspoCRM is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * EspoCRM is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with EspoCRM. If not, see http://www.gnu.org/licenses/.
+ *
+ * The interactive user interfaces in modified source and object code versions
+ * of this program must display Appropriate Legal Notices, as required under
+ * Section 5 of the GNU General Public License version 3.
+ *
+ * In accordance with Section 7(b) of the GNU General Public License version 3,
+ * these Appropriate Legal Notices must retain the display of the "EspoCRM" word.
+ ************************************************************************/
+
+namespace tests\unit\Espo\ORM;
+
+use Espo\ORM\BaseEntity;
+use Espo\ORM\Defs;
+use Espo\ORM\Defs\DefsData;
+use Espo\ORM\EntityCollection;
+use Espo\ORM\Metadata;
+use Espo\ORM\MetadataDataProvider;
+use Espo\Core\ORM\EntityManager;
+
+use PHPUnit\Framework\TestCase;
+
+require_once 'tests/unit/testData/DB/Entities.php';
+
+class CollectionTest extends TestCase
+{
+    protected function setUp(): void
+    {
+        $ormMetadata = include('tests/unit/testData/DB/ormMetadata.php');
+
+        $metadataDataProvider = $this->createMock(MetadataDataProvider::class);
+
+        $metadataDataProvider
+            ->expects($this->any())
+            ->method('get')
+            ->willReturn($ormMetadata);
+
+        $this->metadata = new Metadata($metadataDataProvider);
+        $defsData = new DefsData($this->metadata);
+        $defs = new Defs($defsData);
+
+        $this->entityManager = $this->createMock(EntityManager::class);
+
+        $this->entityManager
+            ->expects($this->any())
+            ->method('getDefs')
+            ->willReturn($defs);
+    }
+
+    /** @noinspection PhpSameParameterValueInspection */
+    private function createEntity(string $entityType): BaseEntity
+    {
+        $defs = $this->metadata->get($entityType);
+
+        return new BaseEntity($entityType, $defs, $this->entityManager);
+    }
+
+    public function testEntityCollectionAppend(): void
+    {
+        $entity1 = $this->createEntity('Account');
+        $entity2 = $this->createEntity('Account');
+        $entity3 = $this->createEntity('Account');
+
+        $collection = new EntityCollection([$entity1]);
+
+        $collection[] = $entity2;
+        $collection->append($entity3);
+
+        $this->assertEquals(3, $collection->count());
+    }
+
+    public function testEntityCollectionIteratorToArray(): void
+    {
+        $entity1 = $this->createEntity('Account');
+        $entity2 = $this->createEntity('Account');
+        $entity3 = $this->createEntity('Account');
+
+        $collection1 = new EntityCollection([$entity1]);
+        $collection2 = new EntityCollection([$entity2, $entity3]);
+
+        $collection = new EntityCollection([
+            ...iterator_to_array($collection1),
+            ...iterator_to_array($collection2),
+        ]);
+
+        $this->assertEquals(3, $collection->count());
+    }
+
+    public function testEntityCollectionUnset(): void
+    {
+        $entity1 = $this->createEntity('Account');
+        $entity2 = $this->createEntity('Account');
+
+        $collection = new EntityCollection([$entity1]);
+
+        $collection[] = $entity2;
+        unset($collection[1]);
+
+        $this->assertEquals(1, $collection->count());
+    }
+}