Throw Exception in Flutter Test

Question

I am following this tutorial for Clean Architecture in flutter

This is my test file

test(
        'should return server failure when call to remote data is unsuccessful',
            () async {
          // arrange
          when(mockRemoteDataSource.getConcreteNumberTrivia(any))
          .thenThrow(ServerException());

          // act
          final result = await repository.getConcreteNumberTrivia(tNumber);

          // assert
          verify(mockRemoteDataSource.getConcreteNumberTrivia(tNumber));
          verifyZeroInteractions(mockLocalDataSource); // <--- this line is failing
          expect(result, equals(Left(ServerFailure()))); // // <--- this line is failing
        },
      );

This is my code

Future<Either<Failure, NumberTrivia>> getConcreteNumberTrivia(int number) async {
    networkInfo.isConnected;

    try {
      final remoteTrivia = await remoteDataSource.getConcreteNumberTrivia(number);
      localDataSource.cacheNumberTrivia(remoteTrivia);
      return Right(remoteTrivia);
    } on ServerException {
      return Left(ServerFailure());
    }
  }

I dont know why but coz of these 2 lines, test case is failing.

verifyZeroInteractions(mockLocalDataSource);
expect(result, equals(Left(ServerFailure())));

I have mentioned in test case to throw a server exception using when and thenThrow but still it goes to this line localDataSource.cacheNumberTrivia(remoteTrivia);. I think this is the cause of the error but I am not quite sure.

I did read the docs but I could not find why is this problem occuring. What am i doing wrong? I am new to TDD in flutter. Thanks in advance :)