addCartMergedNoticeFlash example

$productLineItem1->setStackable(true);
        $productLineItem2->setStackable(true);
        $productLineItem1->setQuantity(1);
        $guestProductQuantity = 5;
        $productLineItem2->setQuantity($guestProductQuantity);

        $previousCart->addLineItems(new LineItemCollection([$productLineItem1, $productLineItem2]));
        $previousCart->markUnmodified();

        $cartMergedEvent = new CartMergedEvent(new Cart('customerToken'), $currentContext, $previousCart);

        $subscriber->addCartMergedNoticeFlash($cartMergedEvent);

        static::assertNotEmpty($infoFlash = $session->getFlashBag()->get('info'));

        static::assertEquals('checkout.cart-merged-hint', $infoFlash[0]);
    }

    /** * @param array<string, mixed> $salesChannelData */
    private function createSalesChannelContext(string $contextToken, array $salesChannelData, ?string $customerId = null): SalesChannelContext
    {