### Question:
PetApi { public Mono<Pet> getPetById(Long petId) throws WebClientResponseException { Object postBody = null; if (petId == null) { throw new WebClientResponseException("Missing the required parameter 'petId' when calling getPetById", HttpStatus.BAD_REQUEST.value(), HttpStatus.BAD_REQUEST.getReasonPhrase(), null, null, null); } final Map<String, Object> pathParams = new HashMap<String, Object>(); pathParams.put("petId", petId); final MultiValueMap<String, String> queryParams = new LinkedMultiValueMap<String, String>(); final HttpHeaders headerParams = new HttpHeaders(); final MultiValueMap<String, String> cookieParams = new LinkedMultiValueMap<String, String>(); final MultiValueMap<String, Object> formParams = new LinkedMultiValueMap<String, Object>(); final String[] localVarAccepts = { "application/xml", "application/json" }; final List<MediaType> localVarAccept = apiClient.selectHeaderAccept(localVarAccepts); final String[] localVarContentTypes = { }; final MediaType localVarContentType = apiClient.selectHeaderContentType(localVarContentTypes); String[] localVarAuthNames = new String[] { "api_key" }; ParameterizedTypeReference<Pet> localVarReturnType = new ParameterizedTypeReference<Pet>() {}; return apiClient.invokeAPI("/pet/{petId}", HttpMethod.GET, pathParams, queryParams, postBody, headerParams, cookieParams, formParams, localVarAccept, localVarContentType, localVarAuthNames, localVarReturnType); } PetApi(); @Autowired  PetApi(ApiClient apiClient); ApiClient getApiClient(); void setApiClient(ApiClient apiClient); Mono<Void> addPet(Pet body); Mono<Void> deletePet(Long petId, String apiKey); Flux<Pet> findPetsByStatus(List<String> status); Flux<Pet> findPetsByTags(Set<String> tags); Mono<Pet> getPetById(Long petId); Mono<Void> updatePet(Pet body); Mono<Void> updatePetWithForm(Long petId, String name, String status); Mono<ModelApiResponse> uploadFile(Long petId, String additionalMetadata, File file); Mono<ModelApiResponse> uploadFileWithRequiredFile(Long petId, File requiredFile, String additionalMetadata);  }### Answer:
@Test public void getPetByIdTest() { Long petId = null; Pet response = api.getPetById(petId).block(); }