Problems with mocking riverpod providers

[Vera-Spoettl]

Describe the bug
I want to write an unit test for a method that is part of a notifier (Provider A). I'll try to explain with a very simple example:

import 'package:riverpod_annotation/riverpod_annotation.dart';
import 'package:test_notifier/provider_b.dart';

part 'provider_a.g.dart';

@riverpod
class ProviderA extends _$ProviderA {
  @override
  int build() {
    return 0;
  }

  void increment() {
    ref.read(providerBProvider.notifier).increment();
  }
}

As you can see, increment calls another notifier's method (ProviderB -> increment).

import 'package:riverpod_annotation/riverpod_annotation.dart';

part 'provider_b.g.dart';

@riverpod
class ProviderB extends _$ProviderB {
  @override
  int build() {
    return 0;
  }

  void increment() {
    state++;
  }
}

I would like to write a test now that verifies if Provider B's method increment was call once.

import 'package:flutter/material.dart';
import 'package:test/test.dart';
import 'package:riverpod/riverpod.dart';
import 'package:test_notifier/provider_a.dart';
import 'package:test_notifier/provider_b.dart';
import 'package:mocktail/mocktail.dart';

class MockProviderB extends AutoDisposeNotifier<int>
    with Mock
    implements ProviderB {
  @override
  int build() {
    return 0;
  }

  @override
  void increment() {
    debugPrint('increment providerB in Mock implementation');
  }
}

void main() {
  late ProviderContainer container;
  MockProviderB mockProviderB = MockProviderB();

  setUp(() {
    container = ProviderContainer(
      overrides: [
        providerBProvider.overrideWith(() => mockProviderB),
      ],
    );
  });

  tearDown(() {
    container.dispose();
  });

  test('ProviderB is called once', () {
    final providerA = container.read(providerAProvider.notifier);
    providerA.increment();
    verify(() => mockProviderB.increment).called(1);
  });
}

To Reproduce

Reproducdable by the code above.

Expected behavior
I would have expected that verify(() => mockProviderB.increment()).called(1); should work fine.

What I get instead is the following:

It looks as if mockProviderB was never called ...

However, when I look at the debug window, I get the following:

So, the mock's implementation was called. It seems as if the override works for the invocation but not for the verify statement.

Can you help me whats wrong in my code? Remi from riverpod told me that I'm using mocktail wrong. So how should I implement a test that checks whether notifier A calls notifier B when only the internal state of the notifier is change and not the public model?

[moderateroni]

two things:

• you have to call the function by using brackets after mockProvider.increment
• you should not implement increment in your mock, because Mock will only do its magic if the implementation is missing

in total this works then:

class MockProviderB extends AutoDisposeNotifier<int> with Mock implements ProviderB {}

void main() {
  late ProviderContainer container;
  MockProviderB mockProviderB = MockProviderB();

  setUp(() {
    container = ProviderContainer(
      overrides: [
        providerBProvider.overrideWith(() => mockProviderB),
      ],
    );
  });

  tearDown(() {
    container.dispose();
  });

  test('ProviderB is called once', () {
    final providerA = container.read(providerAProvider.notifier);
    providerA.increment();
    verify(() => mockProviderB.increment()).called(1);
  });
}