^(.*?)s*((s*d+)s*)?$

using System;
using System.Text.RegularExpressions;

public class Example
{
    public static void Main()
    {
        string pattern = @"^(.*?)s*((s*d+)s*)?$";
        string input = @"Test
Test (1)
Test (1) (2)
Test (1) (2) (3)
Test (1) (2)    (3) (4)
";
        RegexOptions options = RegexOptions.Multiline;

        foreach (Match m in Regex.Matches(input, pattern, options))
        {
            Console.WriteLine("'{0}' found at index {1}.", m.Value, m.Index);
        }
    }
}