How to Mock REST API in unit testing?

Question

I am using RestTemplate exchange HttpMethod.POST method to POST to an endpoint. In my test file I am testing for success of the POST method. However wi

Answer 1

You are testing the logic inside DataTestRepo class, so you should not mock it. RestTemplate is a dependency inside DataTestRepo, so this is exactly what you need to mock. In general it should look like this inside your test:

@InjectMocks
private DataTestRepo DataTestRepo;
@Mock
RestTemplate restTemplate;

Also, you will have to provide a return value for your mocked dependency, like this:

Mockito.when(restTemplate.exchange(ArgumentMatchers.any(), ArgumentMatchers.any(), ArgumentMatchers.any(), ArgumentMatchers.any())).thenReturn(new ResponseEntity<>(yourExpectedDataHere, HttpStatus.OK));
enter code here

This is just a simple example. A good practice would be to check that the arguments passed to your mock equal to the expected ones. One way would be to replace ArgumentMatchers.any() with the real expected data. Another is to verify it separately, like this:

Mockito.verify(restTemplate, Mockito.times(1)).exchange(ArgumentsMatchers.eq(yourExpectedDataHere), ArgumentsMatchers.eq(yourExpectedDataHere), ArgumentsMatchers.eq(yourExpectedDataHere), ArgumentsMatchers.eq(yourExpectedDataHere));

Answer 2

This is a great read on this topic: https://reflectoring.io/spring-boot-web-controller-test/