After migrating flutter code to null-safety, mock objects not accepting `any`

Question

After the release of Flutter 2, I've migrated my code to sdk: '>=2.12.0 <3.0.0' and all codes are "sound null safety" now. But I encountered errors in unit tests with mockito 5.0.0

e.g:

when(mockClient.login(any)).thenThrow(GrpcError.unavailable());

was ok earlier, but now, the compiler shows an error under any, indicating: The argument type 'Null' can't be assigned to the parameter type 'LoginRequest'

I read this link from mockito repo but I hope there is an easier way to write tests for methods with "not nullable" arguments like before.

Does my solution below solve your problem? – Pablito May 23 '21 at 09:23 — Pablito, May 23 '21 at 09:23

score 22 · Answer 1 · answered Jul 15 '21 at 17:40

When assigning the Mock object, it needs to be of the Mock object type, not the BaseClass.


@GenerateMocks(MockSpec<ITransactionRepository>(as: #MockTransactionRepository),
)
void main()
{
    ....
    ITransactionRepository baseObject = MockTransactionRepository();           // wrong
    MockTransactionRepository mockObject = MockTransactionRepository();   // right
    when(baseObject.method(any));     // results in compile error
    when(mockObject.method(any)); // OK
    ...
}

Source: https://github.com/dart-lang/mockito/issues/364

score 9 · Accepted Answer · answered Apr 30 '21 at 17:46

9

See the solution here. You can use the mocktail package which makes it way easier.

With mocktail your code would become

when(() => mockClient.login(any())).thenThrow(GrpcError.unavailable());

answered Apr 30 '21 at 17:46

Pablito

521
4
15

score 6 · Answer 3 · answered Mar 11 '21 at 12:48

any return null and null value is not allowed to be passed to your login method.

It's the main drawback of NNBD, the mocking is much less easy than before.

https://github.com/dart-lang/mockito/blob/master/NULL_SAFETY_README.md#problems-with-typical-mocking-and-stubbing

score 2 · Answer 4 · answered May 13 '22 at 07:43

To deal with null-safety in mockito

step 1: don't create mock classes and implementation manually so delete them

step 2: install build_runner for generating files using dart code

step 3: import 'package:mockito/annotations.dart'; to your test file

step 4: annotate your target class to be mocked with @GenerateMocks([YourClassToBeMocked]) above void main() function

step 5: run build_runner to generate mock with a --delete-conflicting-outputs flag, so in your terminal type: flutter pub run build_runner build --delete-conflicting-outputs. Enabling this option skips the prompt and deletes the files. This should typically be used in continues integration servers and tests, but not otherwise.

step6: after generating mock file import it into your test(it is located in same directory of your test file) and then you are good to go and use any in where method and also use a non-nullable variable in your classes even without implementing it.

for a full answer check out this link

score -2 · Answer 5 · answered Mar 11 '22 at 06:45

The function you are calling in the mocked class, make the argument nullable. If you are mocking this class method:

class Example {
    String method(String str) {}
}

Make the String argument nullable like:

String method(String? str) {}

Hope it works.

After migrating flutter code to null-safety, mock objects not accepting `any`

5 Answers5