Verify positional parameter 'null' not working together with any()

[moderateroni]

Describe the bug
When you have multiple positional parameters of the same (nullable) Type in your mocked Method, you cannot verify that one positional parameter is null and others are any().

To Reproduce
Steps to reproduce the behavior:

This Test will fail, but from my point of view it should not:

import 'package:flutter_test/flutter_test.dart';
import 'package:mocktail/mocktail.dart';

class MockListener extends Mock {
  void call(int? previous, int next);
}

void main() {
  late MockListener listener;

  setUp(() {
    listener = MockListener();
    registerFallbackValue(1);
  });

  test('verify listener is called with any()', () {
    // Arrange
    final previousInt = null;
    final nextInt = 3;

    // Act
    listener(previousInt, nextInt);

    // Assert
    verify(() => listener(null, any())).called(1);
  });
}

Expected behavior
Tests like this should not fail

Additional context
In _is_invocation.dart, there is this line of code in _reconstitutePositionalArgs:
if (positionalArgument == null || positionalArgument == arg._fallbackValue)

shouldn't the first check be removed? i did this and all tests are still successful.

easy workaround of course is to also use a matcher for the first positional argument, so
verify(() => listener(any(that: isNull), any())).called(1);
will work

[felangel]

Hi @moderateroni 👋
Thanks for the issue!

I took a closer look and the fundamental issue is that any() matchers currently don't have any notion of which positional argument they are matching. The suggestion you made doesn't solve this problem, it just happens to fix the one particular case you have here since we match null and then the remaining any() is applied to nextInt.

I'll think some more about this and hopefully can come up with some solutions to the underlying issue.