DecoratorLogger_1

public class MemoryLogger
    {
        public List<LogLine> Log { get; }

        public MemoryLogger()
        {
            Log = new List<LogLine>();
        }
        public void Exception(string message, Exception ex)
        {
            Log.Add(new LogLine(LogLine.SeverityLevels.Error, message, ex));
        }

        public void Info(string message)
        {
            Log.Add(new LogLine(LogLine.SeverityLevels.Info, message));
        }

        public void Warning(string message)
        {
            Log.Add(new LogLine(LogLine.SeverityLevels.Warn, message));
        }

        public override string ToString()
        {
            var sb = new StringBuilder();
            foreach (var logLine in Log)
                sb.AppendLine(logLine.ToString());
            return sb.ToString();
        }
    }

    public class LogLine
    {
        public SeverityLevels Severity { get; }
        public string Message { get; }
        public Exception Exception { get; }

        public enum SeverityLevels
        {
            Debug, Info, Warn, Error
        }
        public LogLine(SeverityLevels severity, string message, Exception exception = null)
        {
            Severity = severity;
            Message = message;
            Exception = exception;
        }

        public override string ToString()
        {
            return $"{Severity}: {Message} {Exception?.Message}";
        }
    }