selected_shipping_method received twice even if multishipping was disabled

[TomashKhamlai]

Preconditions (*)

There were lot of settings. Write a comment if not reproducible

1. Setup Magento to support all the shipping methods or at least UPS

Steps to reproduce (*)

1. Generate Customer token
2. Create empty cart
3. Set shipping address on empty cart
4. Try to set any shipping method and get the error
5. Add simple product to cart with qty 7
6. Try to set the next shipping method

   mutation {
   setShippingMethodsOnCart(
   input: {
     cart_id: "{{ YOUR VALUE }}"
     shipping_methods: {
       cart_address_id: {{ YOUR VALUE }}
       carrier_code: "ups"
       method_code: "GND"
     }
   }
   ) {
   cart {
     shipping_addresses {
       selected_shipping_method {
         carrier_code
         method_code
         label
         amount
       }
       available_shipping_methods {
         carrier_title
         method_title
         price_incl_tax
         base_amount
         price_excl_tax
         amount
       }
     }
   }
   }
   }

7. Disable Multishipping
8. Examine the cart:

   query {
   cart(cart_id: "{{ YOUR VALUE }}")
   {
   shipping_addresses {
     selected_shipping_method {
       carrier_code
       method_code
     }
   }
   }
   }

Expected result (*)

1. selected_shipping_method only once

   {
   "data": {
   "cart": {
     "shipping_addresses": [
       {
         "selected_shipping_method": {
           "carrier_code": ups,
           "method_code": GND
         }
       }
     ]
   }
   }
   }

   Actual result (*)

2. selected_shipping_method only twice

   {
   "data": {
   "cart": {
     "shipping_addresses": [
       {
         "selected_shipping_method": {
           "carrier_code": null,
           "method_code": null
         }
       },
       {
         "selected_shipping_method": {
           "carrier_code": "ups",
           "method_code": "GND"
         }
       }
     ]
   }
   }
   }

[TomashKhamlai]

Not a bug

[TomashKhamlai]

Just a good test case for future checks of #404. @naydav, please verify that Customer can set any number of addresses on preparing cart for checkout and please prepare some expectations for the case when Multishipping was disabled unexpectedly for Customers

[naydav]

We could not consider that is a bug. State of the system was changed during checkout workflow.