Flutter test bloc error type 'Null' is not a subtype of type

Question

I'm testing a bloc method that fetch a list of restaurants fro the api.

here is my code :

import 'package:bloc_test/bloc_test.dart';
import 'package:flutter_test/flutter_test.dart';
import 'package:mobile_app_engineer/blocs/merchant_bloc.dart';
import 'package:mobile_app_engineer/repositories/merchant_repository.dart';
import 'package:mockito/mockito.dart';
import 'package:mobile_app_engineer/models/list_merchants_response.dart';

class MockMerchantRepository extends Mock implements MerchantRepository {}

// Generate a MockClient using the Mockito package.
// Create new instances of this class in each test.
void main() {

late MockMerchantRepository mockMerchantRepository;

setUp((){
  mockMerchantRepository = MockMerchantRepository();
});

List<Merchant> merchantList = [
   Merchant object here    
];

blocTest<MerchantBloc, MerchantState>(
   'Check if merchant fetch return correct data',
   build: () {
   when(mockMerchantRepository.fetchMerchants(1)).thenThrow(NetworkError()); <=== in this line main 101
   return MerchantBloc(mockMerchantRepository);
},
  act: (bloc) => bloc.add(GetMerchantsList(1)),
  expect: () => [MerchantInitial(), GetMerchantsListState(merchantList)],
);

}

I'm getting this error :

type 'Null' is not a subtype of type 'Future<List<Merchant>>'
package:mobile_app_engineer/repositories/merchant_repository.dart 14:26  
MockMerchantRepository.fetchMerchants
test/api_test/fetch_restaurant_test.dart 101:35                          main.<fn>
package:bloc_test/src/bloc_test.dart 176:25                              testBloc.<fn>

Is there something that i'm doing wrong ? thx

Answer 1

Found the solution : it's because of null safety so now i had to add GenerateMocks to generate a mock repository for the api call.

import 'fetch_merchant_test.mocks.dart';

@GenerateMocks([MockMerchantRepository])
void main() {

final mockMerchantRepository = MockMockMerchantRepository();