CartMergedSubscriber example

$request = new Request();
        $request->setSession($session);
        $requestStack = new RequestStack();
        $requestStack->push($request);

        $translator = $this->createMock(TranslatorInterface::class);
        $translator->expects(static::once())
            ->method('trans')
            ->with('checkout.cart-merged-hint')
            ->willReturn('checkout.cart-merged-hint');

        $subscriber = new CartMergedSubscriber($translator, $requestStack);

        $currentContextToken = 'currentToken';
        $currentContext = $this->createSalesChannelContext($currentContextToken, []);

        // Create Guest cart         $previousCart = new Cart($currentContextToken);

        $productId1 = $this->createProduct($currentContext->getContext());
        $productId2 = $this->createProduct($currentContext->getContext());

        $productLineItem1 = new LineItem($productId1, LineItem::PRODUCT_LINE_ITEM_TYPE, $productId1);