test_failed.dart

 
//Here debug console output
Expected: <Instance of 'DataResponse<Utilisateur>'>
  Actual: <null>

package:test_api                                         expect
package:flutter_test/src/widget_tester.dart 369:3        expect
test/repositories/login/login_api_client_test.dart 30:7  main.<fn>.<fn>

// login_api_client_test.dart
class MockNetworkUtil extends Mock implements NetworkUtil<Utilisateur> {}

main() {
  group('LoginApiClient', () {
    NetworkUtil networkUtil;
    LoginApiClient loginApiClient;

    setUp(() {
      networkUtil = MockNetworkUtil();
      loginApiClient = LoginApiClient(networkUtil: networkUtil);
    });

    test("return DataResponse when networkUtil calls succeed", () async {
      var utilisateur = Utilisateur(login: "test", password: "test");
      var dataReq = DataRequest<Utilisateur>(data: utilisateur);

      final expected = DataResponse<Utilisateur>();
      when(networkUtil.post(url: "/user/login", data: dataReq))
          .thenAnswer((_) async => expected);

      var result = await loginApiClient.login(utilisateur);
      expect(result, expected);

    });
  });
   
}

// login_api_client.dart
class LoginApiClient {
  final NetworkUtil<Utilisateur> networkUtil;

  LoginApiClient({this.networkUtil});

  Future<DataResponse<Utilisateur>> login(Utilisateur utilisateur) async {
    DataRequest<Utilisateur> dataRequest = DataRequest<Utilisateur>(data: utilisateur);
    var response = await networkUtil.post(url: "/user/login", data: dataRequest);
    print("response = $response");
    return response;
  }
}

//network_util.dart
class NetworkUtil<T> {
  static final _BASE_URL = "api_url";

  final http.Client httpClient;

  NetworkUtil({this.httpClient});

  Future<DataResponse<T>> post({String url, String tenantID = "", dynamic data}) async {
    
    final response = await httpClient.post(_BASE_URL + url,
        headers: {
          "Content-Type": "application/json; charset=utf-8",
          "tenantID": tenantID
        },
        body: data.toJson());

    if (response.statusCode != 200) {
      throw Exception('error getting http response');
    }  
    return DataResponse<T>.fromJson(json.decode(response.body.toString()));
  }
}