using System;

public class Program

{

    public static void Main()

    {

        var fallback = "0555";

        var tests = new string[] {

            "interim",                      // Test 1

            "567573, Pizzabakeren",         // Test 2 

            " ",                            // Test 3

            null,                           // Test 4

            "5675, 73, Pizzabakeren, 632815"// Test 5

        };

        var expected = new string[] {

            fallback,                       // Test 1

            "567573",                       // Test 2

            fallback,                       // Test 3

            fallback,                       // Test 4

            "5675"                          // Test 5

        };

        int testcount = 1;      

        foreach(var test in tests){

            Console.WriteLine($"Test nr {testcount}");

            Console.WriteLine($"Test successful:  {Test(test, fallback) == expected[testcount - 1]}");

            testcount++;

            Console.WriteLine(string.Empty);

        }

    }

    private static string Test(string ld, string fallback)

    {

        Console.WriteLine($"Testing {ld}");

        if (string.IsNullOrEmpty(ld))

        {

            return fallback;

        }

        string [] lineDescriptionSplit = ld.Split(',', 2);

        return lineDescriptionSplit[0] ?? fallback;

    }

}