Reducer with State Notifier

reducer_notifier.dart

import 'dart:async';

import 'package:state_notifier/state_notifier.dart';

class ReducerNotifier<State> extends StateNotifier<State> {
  final Reducer<State> reducer;
  
  ReducerNotifier(state, this.reducer) : super(state);

  FutureOr<void> dispatch(Action action) async {
    state = await reducer.reduce(state, action);
  }
}

abstract class Action {}

abstract class Reducer<State> {
  FutureOr<State> reduce(State state, Action action);
}

reducer_notifier_test.dart

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

void main() {
  test('adds one to input values', () async {

    final counter = ReducerNotifier(0, CounterReducer());

    await counter.dispatch(IncrementAction());

    expect(counter.debugState, 1);

    await counter.dispatch(IncrementAction());

    expect(counter.debugState, 2);

    await counter.dispatch(DecrementAction());

    expect(counter.debugState, 1);
  });
}

class IncrementAction extends Action {}

class DecrementAction extends Action {}

class CounterReducer extends Reducer<int> {
  @override
  reduce(state, Action action) {
    if (action is IncrementAction) return state + 1;
    if (action is DecrementAction) return state - 1;

    return state;
  }
}