How to test a POSTing method by using an embedded Webserver in Springboot? - spring-boot

Question

I am searching for a way to test a method, which sends a POST request to an external service. The application will NOT be itself a consumable webservice, that is why I didn't implement the shown class below as #RestController, #Controller, #Service, whatever types there may be.
But I don't know how to call the method postNumberPlate() to send a request to an embedded webserver (started in/by/at the unit test) to make some assertions on it. I want to avoid, to install an external webserver.
In other words: Can I start an embedded webserver inside a unit-test and 'tell' it to accept my POST request to inspect and assert the contents?
I already did:
a massive Webresearch (2-3 days?)
read Howto's
check the springboot docs
use an embedded Jetty Server (somehow blocking loop)
declare the Application as Webapplication and setting random port to jetty
experiment with Mockito, MockMVC
read "How to unittest a class using RestTemplate offline?" and compared it to my case, but found,
that it's very old (8y),
I don't know how to implement the parent interface, which is pretty huge
that the question and answers are too generic to deduce a solution for my case
it's not answering the embedded testing webserver problem I included.
The Class to be tested:
public class RestfulClient {
private RestTemplate restTemplate = new RestTemplate();
private HttpHeaders headers = new HttpHeaders();
#Value("${kafkaeskadapter.uri}")
private String destinationURL;
public RestfulClient() {}
public ResponseEntity<String> postNumberPlate(String key, CamImage camImage) {
LinkedMultiValueMap<String, Object> map = new LinkedMultiValueMap<>();
map.add("numplate", camImage.getIdentifier());
headers.setContentType(MediaType.MULTIPART_FORM_DATA);
HttpEntity<LinkedMultiValueMap<String, Object>> requestEntity = new HttpEntity<LinkedMultiValueMap<String,
Object>>(map, headers);
ByteArrayResource resource = new ByteArrayResource(camImage.getData()) {
/**
* IMPORTANT!!! Otherwise I receive a BAD REQUEST
* #return
*/
#Override
public String getFilename() {
return camImage.getIdentifier() + ".png";
}
};
map.add("image", resource);
ResponseEntity<String> result = restTemplate.exchange(destinationURL, HttpMethod.POST,
requestEntity, String.class);
return result;
}
}
I hope I could clarify my question a bit.

Answer 1

A solution is to write a simple light-weight Webservice Endpoint and include it into your Run Configuration of your IDE. I made a separate mini project and would add further methods if needed, e.g. to accept different media.
Prior to run the actual unit tests, it is possible to configure the start of the Endpoint and return a meaningful ResponseEntity. The result can be inspected et voilà, assertions are possible.
A word about StackOverflow user arrogance: #Raedwald, after reading and trying, the answers in the linked question are not really helpful, but involve a lot of knowlegde about the stuff, and I have no one around of my colleagues, which could ever assist at programming. So it wasn't helpful to flag my question for deletion.