testDbListener.cs

    public class TestDbListener : DbListener
    {
        private readonly BlockingCollection<List<DbListenerEvent>> _events = new BlockingCollection<List<DbListenerEvent>>();
        private readonly List<DbListenerEvent> _triggerErrorFlag = new List<DbListenerEvent>();
        private Exception _error;

        public TestDbListener([NotNull] IOptions<DbListenerOptions> options) : base(options)
        {
        }

        public override Task StopAsync(CancellationToken token)
        {
            // Wake up WaitForNotificationsAsync to exit run loop
            _events.CompleteAdding();
            return base.StopAsync(token);
        }

        protected override async Task<IEnumerable<DbListenerEvent>> WaitForNotificationsAsync(CancellationToken token)
        {
            var data = await Task.Run(() => _events.Take(), token);
            if (data == _triggerErrorFlag)
            {
                throw _error;
            }

            return data;
        }

        protected override Task ConnectAsync(CancellationToken token)
        {
            return Task.CompletedTask;
        }

        public void PublishEvent(params DbListenerEvent[] e)
        {
            _events.Add(new List<DbListenerEvent>(e));
        }

        public void TriggerError(Exception e)
        {
            _error = e;
            _events.Add(_triggerErrorFlag);
        }
    }