ISSUE-5021 fixed guest checkout for custom shipping carrier with underscores

Author: vovsky

app/code/Magento/Checkout/Model/GuestPaymentInformationManagement.php

@@ -190,9 +190,8 @@ private function limitShippingCarrier(Quote $quote) : void
     {
         $shippingAddress = $quote->getShippingAddress();
         if ($shippingAddress && $shippingAddress->getShippingMethod()) {
-            $shippingDataArray = explode('_', $shippingAddress->getShippingMethod());
-            $shippingCarrier = array_shift($shippingDataArray);
-            $shippingAddress->setLimitCarrier($shippingCarrier);
+            $shippingRate = $shippingAddress->getShippingRateByCode($shippingAddress->getShippingMethod());
+            $shippingAddress->setLimitCarrier($shippingRate->getCarrier());
         }
     }
 }

app/code/Magento/Checkout/Test/Unit/Model/GuestPaymentInformationManagementTest.php

@@ -273,7 +273,7 @@ public function testSavePaymentInformationAndPlaceOrderWithLocalizedException()
      */
     private function getMockForAssignBillingAddress(
         int $cartId,
-        \PHPUnit_Framework_MockObject_MockObject  $billingAddressMock
+        \PHPUnit_Framework_MockObject_MockObject $billingAddressMock
     ) : void {
         $quoteIdMask = $this->createPartialMock(QuoteIdMask::class, ['getQuoteId', 'load']);
         $this->quoteIdMaskFactoryMock->method('create')
@@ -287,9 +287,11 @@ private function getMockForAssignBillingAddress(
         $billingAddressId = 1;
         $quote = $this->createMock(Quote::class);
         $quoteBillingAddress = $this->createMock(Address::class);
+        $shippingRate = $this->createPartialMock(\Magento\Quote\Model\Quote\Address\Rate::class, []);
+        $shippingRate->setCarrier('flatrate');
         $quoteShippingAddress = $this->createPartialMock(
             Address::class,
-            ['setLimitCarrier', 'getShippingMethod']
+            ['setLimitCarrier', 'getShippingMethod', 'getShippingRateByCode']
         );
         $this->cartRepositoryMock->method('getActive')
             ->with($cartId)
@@ -309,6 +311,9 @@ private function getMockForAssignBillingAddress(
         $quote->expects($this->once())
             ->method('setBillingAddress')
             ->with($billingAddressMock);
+        $quoteShippingAddress->expects($this->any())
+            ->method('getShippingRateByCode')
+            ->willReturn($shippingRate);
         $quote->expects($this->once())
             ->method('setDataChanges')
             ->willReturnSelf();