How to mock a service calling another service using resttemplate in spring-boot?

Question

Good Afternoon to the experts,

I have a requirement where I will be invoking sequential calling of 3 REST APIs as part of a single client call GET /offers to retrieve offers available for each product in different aisles of a department store as below

1. Get all the aisles in a department store /aisels
2. Get all the products in an aisle /aisles/{aisleID}/products

3. Get all the offers for the product /product/{productId/offers

   To do this from my @Service class using the RestTemplate exchange method:

   ResponseEntity aisles= restTemplate.exchange(url, HttpMethod.GET, requestEntity, Aisles.class);

Then retrieve each aisleId in a loop and invoke the 2nd API to get the Products

ResponseEntity<Products> products= restTemplate.exchange(url,
                    HttpMethod.GET, requestEntity, Products.class);

Then retrieve each productId in a loop and invoke the 3rd API to get the Offers

Finally collate all the responses to send the list of offers to the client.

Now, I am new to mockito framework for writing the JUnits. And my service class got a single method named retrieveAllOffers() in which I have the 3 exchange methods as above.

I was wondering how could I mock these 3 calls in my Junit to get a successful response scenario.

Your help is highly appreciated.

Answer 1

Instead of mocking the rest template you can mock the response of the service only. To do that you can use Wiremock ( http://wiremock.org/) which provides an api to stub calls on specific URLS and mock their responses to whatever you like and verify that they were called.

For your case you would need 3 stubs, one for each exchange. For example for this method restTemplate.exchange(url, GET, requestEntity, Products.class); that you provided a stub would look like

stubFor(get(urlEqualTo("yourUrl"))
  .willReturn(aResponse()
    .withStatus(200)
    .withBody(new ObjectMapper().writeValueAsString(yourResponseObject)
    .withHeader("Content-Type", MediaType.APPLICATION_JSON_VALUE))

note that your url will need to point its server where wiremock is running ( if you use the java dependency and junit rule it will be localhost:wiremockPort )

the setup is pretty straight forward as you need to add a single rule to your test

@Rule public WireMockRule wireMockRule = new WireMockRule(options().dynamicPort()); have a look here for the configure of the rule http://wiremock.org/docs/configuration/

and in the end you verify that your stubs where called with

verify(getRequestedFor(urlEqualTo("/yourUrl"))
  .withRequestBody(equalTo(new ObjectMapper().writeValueAsString(theObjectThatShouldBePosted))));

Hope that helped!