How to unit test spring BatchLoaderRegistry with HttpGraphQlTester in SpringBootTest

Question

I am trying to write a unit test using HttpGraphQlTester for the graphQL project, the controller for the project is given below which initializes BatchLoaderRegistry.

public InboundOrderController(BatchLoaderRegistry batchLoaderRegistry) {
batchLoaderRegistry.<String, List<ShipperBooking>>forName("shipperBookingDataLoader")
        .registerMappedBatchLoader((Set<String> orderIds, BatchLoaderEnvironment env) ->
            Mono.just(shipperBookingService.getShipperBookingByOrderIds(orderIds))
        );
  }

This shipperBookingDataLoader created in the constructor is being used in the method as given below in the same class.

@SchemaMapping(typeName = "InboundOrder")
  public LineItemsQuantitySummary orderLineItemsQuantitySummary( DataLoader<String, List<ShipperBooking>> shipperBookingDataLoader) {
    var shipperBookingsList = shipperBookingDataLoader.load(orderId);
}

The test class constructor is this.

InboundOrderGraphQLTest(@Autowired HttpGraphQlTester graphQlTester) {
    this.graphQlTester = graphQlTester;
    authenticatedTester = graphQlTester
        .mutate()
        .webTestClient(
            client -> client.defaultHeader("x-selected-supplier-id", String.valueOf(SUPPLIER_ID)))
        .build();
  }

The requirement is to inject shipperBookingDataloader instance in the above class method orderLineItemQuantitySummary through the test method and mock it's behavior.

@Test
  void testOrderLineItemQuantitySummaryForInboundOrder() {

    var orderId = "1";
    var expectedShipperBooking = mockShipperBooking().build();
    var expectedInboundOrder = mockInboundOrderBuilder(orderId).build();

    var inboundOrderLineItem = Collections.singletonList(
        new InboundOrderLineItem("10", 20, "63692157",
            "RUYE1036.68842645", "HB-01-A0111", "", 18, 15));

    when(inboundOrderService.getByOrderIdForSupplier(orderId, SUPPLIER_ID)).thenReturn(
        expectedInboundOrder);
    when(inboundOrderService.getInboundOrderLineItems(orderId)).thenReturn(inboundOrderLineItem);

    CompletableFuture<List<ShipperBooking>> shipperBookingsFuture = CompletableFuture.completedFuture(
        Collections.singletonList(expectedShipperBooking));

    when(shipperBookingService.getTotalShippedQuantity(inboundOrderLineItem,
        shipperBookingsFuture, "1"))
        .thenReturn(CompletableFuture.completedFuture(18));

    when(shipperBookingService.getTotalReceivedQuantity(inboundOrderLineItem,
        shipperBookingsFuture, "1")).thenReturn(CompletableFuture.completedFuture(15));

    var expectedJson = """
            {
                    "orderLineItemsQuantitySummary": {
                      "totalPlannedQuantity": %d,
                      "totalReceivedQuantity": %d,
                      "totalShippedQuantity": %d
                    }
                }
        """.formatted(inboundOrderLineItem.get(0).plannedQuantity(),
        inboundOrderLineItem.get(0).receivedAtDestinationQuantity(),
        inboundOrderLineItem.get(0).shippedFromOriginQuantity());

    authenticatedTester
        .document("""
            {
                inboundOrder(id: "1") {
                  orderLineItemsQuantitySummary {
                    totalPlannedQuantity
                    totalReceivedQuantity
                    totalShippedQuantity
                  }
                }
              }   
            """).execute()
        .path("inboundOrder").matchesJson(expectedJson);
  }