How to test Sum Double values with Junit and mockito?

Question

I have created a function within my Java, Spring Boot controller which allows me to get sum value of data depending on parameter, this works great. However I have difficulties understanding what would be the best way of testing this function with Junit and Mockito? As of yet I have created a test function which returns me value of one specific array field. How am I able to return a value within .thenReturn() which is summed depending on given serviceID? Any help or suggestions to any other useful post would be appreciated as I wasn't able to find anything relevant or Im looking at wrong places. Thanks

Below I have showed my function which is within my controller

@GetMapping("/orders/test/{serviceId}")
public Double findRevenueByService(@PathVariable Long serviceId){
    log.info("Start of findRevenueByService method {}", serviceId);
    return repository.findPaymentRevenue(serviceId);
}

Query within repository

@Query("select SUM(o.amount) from ORDERS o where o.serviceId = :serviceId")
Double findPaymentRevenue(@Param("serviceId") Long serviceId);

TestController

package PPBackend.controller;

import PPBackend.domain.Order;
import PPBackend.repository.OrderRepository;

import lombok.extern.slf4j.Slf4j;

import org.junit.After;
import org.junit.Before;
import org.junit.Test;
import org.mockito.InjectMocks;
import org.mockito.Mock;
import org.mockito.MockitoAnnotations;


import org.springframework.http.MediaType;
import org.springframework.test.web.servlet.MockMvc;
import org.springframework.test.web.servlet.setup.MockMvcBuilders;

import java.time.LocalDateTime;
import java.util.ArrayList;

import java.util.List;

import static org.mockito.Mockito.when;
import static org.springframework.test.web.servlet.request.MockMvcRequestBuilders.get;

import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.*;
import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.jsonPath;

@Slf4j
public class OrdersControllerTest {    
    @InjectMocks
    private OrdersController controller;    
    private MockMvc mockMvc;    
    @Mock
    private OrderRepository repository;    
    private List<Order> orders = new ArrayList<>();    
    @Before
    public void setUp() {
        MockitoAnnotations.initMocks(this);
        this.mockMvc = MockMvcBuilders.standaloneSetup(controller).build();
        orders.add(new Order(1L,1L,10.00, 50.00,LocalDateTime.now(),LocalDateTime.now()));
        orders.add(new Order(2L,2L,20.00, 50.00,LocalDateTime.now(),LocalDateTime.now()));
        orders.add(new Order(3L,1L,30.00, 50.00,LocalDateTime.now(),LocalDateTime.now()));
        orders.add(new Order(4L,3L,40.00, 50.00,LocalDateTime.now(),LocalDateTime.now()));
        orders.add(new Order(5L,1L,50.00, 50.00,LocalDateTime.now(),LocalDateTime.now()));
    }

    @After
    public void tearDown() {
        orders = new ArrayList<>();
    }

    @Test
    public void findRevenueByService() throws Exception {
        final Long serviceId = 1L;
        when(repository.findPaymentRevenue(serviceId)).thenReturn(orders.get(0).getAmount());
        this.mockMvc.perform(get("/api/test/" + serviceId)).andExpect(status().isOk())
                .andExpect(content().contentType(MediaType.APPLICATION_JSON_UTF8_VALUE))
                .andExpect(jsonPath("$").isNotEmpty())
                .andExpect(jsonPath("$").value(10.00))
                .andExpect(status().isOk());
    }
}

Domain Object

private Long id;
private Long serviceId;
private Double amount;
private Double credit;
private LocalDateTime created;
private LocalDateTime lastEdited;

Answer 1

solved it by using Java8: sum values from specific field of the objects in a list as a reference, needed to make slight amendments