Unable to Mock RestTemplate.exchange

Question

As part of TDD i want to be able to test every portion of my SpringBoot rest application. However i am unable to mock external calls.

Application structure
1. Few rest endpoints which internally call external rest endpoints.
2. All calls to external endpoints are orchestrated through a local http client which utilizes RestTemplate as httpClient.

@RunWith(SpringRunner.class)  

@SpringBootTest(webEnvironment = WebEnvironment.MOCK, classes = TestDrivenDevelopmentWithJavaApplication.class)  

public class TestDrivenDevelopmentWithJavaApplicationTests {
@Autowired
private WebApplicationContext webApplicationContext;
private MockMvc mockMvc;
@MockBean
private RestTemplate client;

@Before
public void setup() throws Exception {
    mockMvc = MockMvcBuilders.webAppContextSetup(webApplicationContext).build();
    Structure1Root category = new Structure1Root();
    Category cat = new Category();
    cat.setCategoryName("Test1");
    cat.setDescription("Test");
    category.setD(cat);

    Mockito.when(client.exchange(
            ArgumentMatchers.eq("https://services.odata.org/V2/Northwind/Northwind.svc/Products(1)?$format=json"),
            ArgumentMatchers.eq(HttpMethod.GET), ArgumentMatchers.eq(null),
            ArgumentMatchers.eq(Structure1Root.class)))
            .thenReturn(new ResponseEntity<Structure1Root>(category, HttpStatus.OK));
}

@Test
public void testendpoint1() throws Exception {
    mockMvc.perform(MockMvcRequestBuilders.get("/api/endpoint1?token=1").contentType(MediaType.APPLICATION_JSON))
            .andExpect(content().string(org.hamcrest.Matchers.containsString("Test1")));

}

}

Even though i have setup the mock on client.exchange(RestTemplate.exchange), i see response returned by client.exchange is null and not the response specified in thenReturn

Controller Code

@RestController
@RequestMapping(path = Endpoint.base)
public class Endpoint {
    public static final String base = "/api";
    @Autowired
    MyHttpClient<Structure2Root> client;
    @Autowired
    MyHttpClient<Structure1Root> Cclient;

    @GetMapping(path = "/endpoint1")
    public ResponseEntity<Structure2Root> callEndpt1(@RequestParam String token) {
        Response<Structure2Root> resp = client
                .execute("https://services.odata.org/V2/Northwind/Northwind.svc/Products(1)?$format=json", Structure2Root.class);
        return new ResponseEntity<Structure2Root>(resp.getResponse(), HttpStatus.OK);
    }

    @GetMapping(path = "/endpoint2")
    public ResponseEntity<Structure1Root> callEndpt2(@RequestParam String token) {
        Response<Structure1Root> resp = Cclient.execute(
                "https://services.odata.org/V2/Northwind/Northwind.svc/Categories(1)?$format=json", Structure1Root.class);
        return new ResponseEntity<Structure1Root>(resp.getResponse(),HttpStatus.OK);
    }

}

And finally, local http client code

@Service
public class MyHttpClient<O> {
    @Autowired
    RestTemplate client;

    public MyHttpClient() {
        // TODO Auto-generated constructor stub
    }

    public Response<O> execute(String url, Class<O> generic) {
        ResponseEntity<O> resp = client.exchange(url, HttpMethod.GET, null, generic);
        return new Response<O>(resp.getStatusCode(), resp.getBody());
    }

}

this client.execute is what i intend to intercept in the first code block

However never seems to work and always returns a null. The Git Repo

Regards,
Veera

Answer 1

You have used the wrong object while mocking. You should be using Structure2Root rather then Structure1Root

The correct test class is below which is working perfectly fine.

package com.demo.samples.tdd;

import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.content;
import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.status;

import com.demo.samples.tdd.responses.Product;
import com.demo.samples.tdd.responses.Structure2Root;
import org.junit.Before;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.mockito.ArgumentMatchers;
import org.mockito.Mockito;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.boot.test.context.SpringBootTest.WebEnvironment;
import org.springframework.boot.test.mock.mockito.MockBean;
import org.springframework.http.HttpMethod;
import org.springframework.http.HttpStatus;
import org.springframework.http.MediaType;
import org.springframework.http.ResponseEntity;
import org.springframework.test.context.junit4.SpringRunner;
import org.springframework.test.web.servlet.MockMvc;
import org.springframework.test.web.servlet.request.MockMvcRequestBuilders;
import org.springframework.test.web.servlet.setup.MockMvcBuilders;
import org.springframework.web.client.RestTemplate;
import org.springframework.web.context.WebApplicationContext;

import com.demo.samples.tdd.responses.Category;
import com.demo.samples.tdd.responses.Structure1Root;

@RunWith(SpringRunner.class)

@SpringBootTest(webEnvironment = WebEnvironment.MOCK, classes = TestDrivenDevelopmentWithJavaApplication.class)
public class TestDrivenDevelopmentWithJavaApplicationTests {
    @Autowired
    private WebApplicationContext webApplicationContext;
    private MockMvc mockMvc;
    @MockBean
    private RestTemplate client;

    @Before
    public void setup() throws Exception {
        mockMvc = MockMvcBuilders.webAppContextSetup(webApplicationContext).build();
//      Structure1Root category = new Structure1Root();
//      Category cat = new Category();
//      cat.setCategoryName("Test1");
//      cat.setDescription("Test");
//      category.setD(cat);
//
//      Mockito.when(client.exchange(
//              ArgumentMatchers.eq("https://services.odata.org/V2/Northwind/Northwind.svc/Products(1)?$format=json"),
//              ArgumentMatchers.eq(HttpMethod.GET), ArgumentMatchers.eq(null),
//              ArgumentMatchers.eq(Structure1Root.class)))
//              .thenReturn(new ResponseEntity<Structure1Root>(category, HttpStatus.OK));


        Structure2Root category2 = new Structure2Root();
        Product product = new Product();
        product.setProductName("Test1");
        product.setUnitPrice("1");
        category2.setD(product);

        Mockito.when(client.exchange(
                ArgumentMatchers.eq("https://services.odata.org/V2/Northwind/Northwind.svc/Products(1)?$format=json"),
                ArgumentMatchers.eq(HttpMethod.GET), ArgumentMatchers.eq(null),
                ArgumentMatchers.eq(Structure2Root.class)))
                .thenReturn(new ResponseEntity<Structure2Root>(category2, HttpStatus.OK));


    }

    @Test
    public void testendpoint1() throws Exception {
        mockMvc.perform(MockMvcRequestBuilders.get("/api/endpoint1?token=1").contentType(MediaType.APPLICATION_JSON))
                .andExpect(content().string(org.hamcrest.Matchers.containsString("Test1")));

    }

}