Springboot Mockito : Mocked service method returning empty body - spring

Question

I have the following jersey controller.
#POST
#ApiOperation(value = "", response = Certification.class)
public Response addCertification(#Valid CertificationRequest request) {
return Response.ok(certificationService.addCertification(request)).build();
}
I have then developed the following test using Mockito and SpringRunner.
#Test
public void givenValidToken_whenAddingCertification_thenCorrect() {
CertificationRequest certificationRequest = new CertificationRequest();
certificationRequest.setName("name");
Certification certification = new Certification();
when(certificationService.addCertification(certificationRequest)).thenReturn(certification);
given()
.contentType(ContentType.JSON)
.body(certificationRequest)
.when()
.post("/certifications")
.then()
.assertThat()
.statusCode(200)
.contentType(ContentType.JSON)
.log()
.all();
}
Written just like that, I receive the following error when it is executed.
HTTP/1.1 200
X-Content-Type-Options: nosniff
X-XSS-Protection: 1; mode=block
Cache-Control: no-cache, no-store, max-age=0, must-revalidate
Pragma: no-cache
Expires: 0
X-Frame-Options: DENY
Content-Length: 0
Date: Fri, 26 Jun 2020 18:33:35 GMT
java.lang.AssertionError: 1 expectation failed.
Expected content-type "JSON" doesn't match actual content-type "".
On the other hand, if I add null in place of certificationRequest and send an empty body in RestAssured , it works fine.
Why does it return an empty body when sent with a request body ?

Answer 1

At least one of your problems is the following:
when(certificationService.addCertification(certificationRequest)).thenReturn(certification);
You need a Matcher instead of certificationRequest. If you want to match any Request you can use ArgumentMatchers.any(). If you want to check for a specific Request you can use ArgumentMatchers.eq(certificationRequest). Note that ArgumentMatchers.eq(...) will only work if you've provided a valid equals method (Or if you pass exactly the same argument, afair).
So for example:
when(certificationService.addCertification(ArgumentMatchers.eq(certificationRequest))).thenReturn(certification);
If that doesn't solve your problem, I would try to print the response and check what you get there.