Bloc or Cubit test helper, without requiring bloc_test package

bloc_testing.dart

import 'package:mocktail/mocktail.dart';
import 'package:meta/meta.dart';
import 'package:bloc/bloc.dart';
import 'dart:async';
import 'package:test/test.dart';

abstract class Callable<T> {
  void call([T? arg]) {}
}

class MockCallable<T> extends Mock implements Callable<T> {}

/// Tests a cubit by making assertions on a state field or the state as a whole
///
/// [build] a closure returning the bloc or cubit under test
/// [stateField] the field we want to make assertions on
/// [act] a closure passing the bloc or cubit under test allowing specific events or actions to be triggered
/// [arrange] useful for mocking specific behaviours prior to calling any actions on the bloc or cubit
/// [assertions] create assertions on the emited values as specified by stateField property selector
@isTest
void cubitTest<P, S, B extends BlocBase<S>>(
  String description, {
  required B Function() build,
  required FutureOr Function(B) act,
  required P Function(S) stateField,
  Function? arrange,
  Function(P)? inspect,
  required void Function(MockCallable<P> updatesWith) assertions,
}) async {
  test(description, () async {
    final expectation = MockCallable<P>();
    arrange?.call();
    final bloc = build();
    bloc.stream.listen((S state) {
      final focusedProperty = stateField(state);
      inspect?.call(focusedProperty);
      expectation(focusedProperty);
    });

    await act(bloc);
    await bloc.close();

    assertions(expectation);
  });
}