serverpod-offline-sync/packages/serverpod_offline_sync/test/utils/once_test.dart

import 'dart:async';

import 'package:serverpod_offline_sync/src/utils/once.dart';
import 'package:test/test.dart';

void main() {
  group('Given an action run once,', () {
    late Once once;
    late int runs;
    late Completer<void> gate;

    setUp(() {
      once = Once();
      runs = 0;
      gate = Completer<void>();
    });

    Future<void> action() async {
      runs++;
      await gate.future;
    }

    test('when asked while it runs and after, then it runs once and every '
        'caller awaits that run.', () async {
      final first = once.run(action);
      final meanwhile = once.run(action);
      gate.complete();
      await Future.wait([first, meanwhile]);
      await once.run(action);

      expect(runs, 1);
    });

    test('when its run fails, then the next caller runs it again.', () async {
      final failing = once.run(() async {
        runs++;
        throw StateError('failed');
      });
      await expectLater(failing, throwsStateError);

      gate.complete();
      await once.run(action);

      expect(runs, 2);
    });
  });
}