### Question:
FakeApi { public Mono<String> fakeOuterStringSerialize(String body) throws WebClientResponseException { Object postBody = body; final Map<String, Object> pathParams = new HashMap<String, Object>(); 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 = { "*/*" }; final List<MediaType> localVarAccept = apiClient.selectHeaderAccept(localVarAccepts); final String[] localVarContentTypes = { }; final MediaType localVarContentType = apiClient.selectHeaderContentType(localVarContentTypes); String[] localVarAuthNames = new String[] { }; ParameterizedTypeReference<String> localVarReturnType = new ParameterizedTypeReference<String>() {}; return apiClient.invokeAPI("/fake/outer/string", HttpMethod.POST, pathParams, queryParams, postBody, headerParams, cookieParams, formParams, localVarAccept, localVarContentType, localVarAuthNames, localVarReturnType); } FakeApi(); @Autowired  FakeApi(ApiClient apiClient); ApiClient getApiClient(); void setApiClient(ApiClient apiClient); Mono<Void> createXmlItem(XmlItem xmlItem); Mono<Boolean> fakeOuterBooleanSerialize(Boolean body); Mono<OuterComposite> fakeOuterCompositeSerialize(OuterComposite body); Mono<BigDecimal> fakeOuterNumberSerialize(BigDecimal body); Mono<String> fakeOuterStringSerialize(String body); Mono<Void> testBodyWithFileSchema(FileSchemaTestClass body); Mono<Void> testBodyWithQueryParams(String query, User body); Mono<Client> testClientModel(Client body); Mono<Void> testEndpointParameters(BigDecimal number, Double _double, String patternWithoutDelimiter, byte[] _byte, Integer integer, Integer int32, Long int64, Float _float, String string, File binary, LocalDate date, OffsetDateTime dateTime, String password, String paramCallback); Mono<Void> testEnumParameters(List<String> enumHeaderStringArray, String enumHeaderString, List<String> enumQueryStringArray, String enumQueryString, Integer enumQueryInteger, Double enumQueryDouble, List<String> enumFormStringArray, String enumFormString); Mono<Void> testGroupParameters(Integer requiredStringGroup, Boolean requiredBooleanGroup, Long requiredInt64Group, Integer stringGroup, Boolean booleanGroup, Long int64Group); Mono<Void> testInlineAdditionalProperties(Map<String, String> param); Mono<Void> testJsonFormData(String param, String param2); Mono<Void> testQueryParameterCollectionFormat(List<String> pipe, List<String> ioutil, List<String> http, List<String> url, List<String> context);  }### Answer:
@Test public void fakeOuterStringSerializeTest() { String body = null; String response = api.fakeOuterStringSerialize(body).block(); }