Fix for Unit Tests

Author: Vitalii Tychenok

app/code/Magento/Multishipping/Controller/Checkout/Plugin.php

@@ -34,8 +34,9 @@ public function __construct(\Magento\Checkout\Model\Cart $cart)
      */
     public function beforeExecute(\Magento\Framework\App\Action\Action $subject)
     {
-        if ($this->cart->getQuote()->getIsMultiShipping()) {
-            $this->cart->getQuote()->setIsMultiShipping(0);
+        $quote = $this->cart->getQuote();
+        if ($quote->getIsMultiShipping()) {
+            $quote->setIsMultiShipping(0);
             $this->cart->saveQuote();
         }
     }

app/code/Magento/Multishipping/Test/Unit/Controller/Checkout/PluginTest.php

@@ -4,6 +4,9 @@
  * Copyright © Magento, Inc. All rights reserved.
  * See COPYING.txt for license details.
  */
+
+declare(strict_types=1);
+
 namespace Magento\Multishipping\Test\Unit\Controller\Checkout;
 
 use Magento\Multishipping\Controller\Checkout\Plugin;
@@ -30,16 +33,27 @@ protected function setUp()
         $this->cartMock = $this->createMock(\Magento\Checkout\Model\Cart::class);
         $this->quoteMock = $this->createPartialMock(
             \Magento\Quote\Model\Quote::class,
-            ['__wakeUp', 'setIsMultiShipping']
+            ['__wakeUp', 'setIsMultiShipping', 'getIsMultiShipping']
         );
         $this->cartMock->expects($this->once())->method('getQuote')->will($this->returnValue($this->quoteMock));
         $this->object = new \Magento\Multishipping\Controller\Checkout\Plugin($this->cartMock);
     }
 
-    public function testExecuteTurnsOffMultishippingModeOnQuote()
+    public function testExecuteTurnsOffMultishippingModeOnMultishippingQuote(): void
     {
         $subject = $this->createMock(\Magento\Checkout\Controller\Index\Index::class);
+        $this->quoteMock->expects($this->once())->method('getIsMultiShipping')->willReturn(1);
         $this->quoteMock->expects($this->once())->method('setIsMultiShipping')->with(0);
+        $this->cartMock->expects($this->once())->method('saveQuote');
+        $this->object->beforeExecute($subject);
+    }
+
+    public function testExecuteTurnsOffMultishippingModeOnNotMultishippingQuote(): void
+    {
+        $subject = $this->createMock(\Magento\Checkout\Controller\Index\Index::class);
+        $this->quoteMock->expects($this->once())->method('getIsMultiShipping')->willReturn(0);
+        $this->quoteMock->expects($this->never())->method('setIsMultiShipping');
+        $this->cartMock->expects($this->never())->method('saveQuote');
         $this->object->beforeExecute($subject);
     }
 }