Junit test jsonprocessingexception

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Java

Spring

Hi,
I have problem testing JsonProcessingException, can someone help me please?

Here is the code I want to test

@GetMapping("/find-something")
    public Something findSomething(@RequestParam String exampleString) throws CustomExceptionWeb, JsonProcessingException {
        CustomClass customClass = objectMapper.readValue(exampleString, CustomClass.class);
        return serviceWeb.findBy(customClass);
    }

Here is the test method :

private static final String BASE_URL = "/sample/api/example/find-something";

@Autowired
    private MockMvc mvc;

 @MockBean
    private ObjectMapper objectMapper;

@Test
void expectToThrowWhenParamIsInvalid() throws Exception {
final String ueryParams = "?customFakeName=\"\"name\":\"fakeItTillYouMakeIt\:\"desc\"\"\n";


when(objectMapper.readValue(anyString(), eq(CustomClas.class))).thenThrow(JsonProcessingException.class);
        RequestBuilder requestBuilder = MockMvcRequestBuilders.get(BASE_URL + ueryParams);

        try {
            mvc.perform(requestBuilder);
            fail();
        } catch (NestedServletException e) {
            System.out.println("Testing = " + e.getRootCause());
            assertTrue(e.getRootCause() instanceof JsonProcessingException);
        }
}

JsonProcessingException it's printing error :

com.fasterxml.jackson.core.JsonProcessingException: N/A

I'm trying to send invalid json string so when objectMapper start mapping string to class throw JsonProcessingException error.

Tnx.

What I have tried:

I tried almoast everything.

When I'm testing

RuntimeException

, test is ok...