// class UtilService code
 
class UtilService {
    boolean transactional = true
    Integer calculatePrice(Item item, Integer vat, Integer profit) {
        return item.price * vat * profit
    }
}

// ItemService class code
 
class ItemService {
    boolean transactional = true
    def utilService
    Integer calculateCost(Item item,Integer quantity) {
        Integer price = utilService.calculatePrice(item,5,8)
        Integer totalCost = price * quantity
        return totalCost
    }
}

  void test_calculateCost() {
 // Step-1: Mocking the domain class
        def instance = [new Item()]
        mockDomain(Item, instance)
 
//Step-2: Mocking the service and its method used in the function that has to be tested
        def otherService = mockFor(UtilService)
        otherService.demand.calculatePrice(1) {l,m, n -> return 150}
 
// Step-3: creating the instance of our service
        def itemService = new ItemService()
        itemService.utilService = otherService.createMock()
 
// Step-4: Calling the method to be tested
        def amount = itemService.calculateCost(instance[0],10)
 
        assertEquals 1500, amount
    }