Print the source filename and linenumber in C#

If you wanted to write your own version of Debug.Assert, then here's a more complete answer:

// CC0, Public Domain
using System.Diagnostics;
using System.Runtime.CompilerServices;
using System;

public static class Logger {
    [Conditional("DEBUG")]  
    public static void Assert(bool condition, string msg,
            [CallerFilePath] string file = "",
            [CallerMemberName] string member = "",
            [CallerLineNumber] int line = 0
            )
    {
        // Debug.Assert opens a msg box and Trace only appears in
        // a debugger, so implement our own.
        if (!condition)
        {
            // Roughly follow style of C# error messages:
            // > ideone.cs(14,11): error CS1585: Member modifier 'static' must precede the member type and name
            Console.WriteLine($"{file}({line}): assert: in {member}: {msg}");
            // Or more precisely match style with a fake error so error-parsing tools will detect it:
            // Console.WriteLine($"{file}({line}): warning CS0: {msg}");
        }
    }
}

class Program {
    static void Main(string[] args) {
        Logger.Assert(1+1 == 4, "Why not!");
    }
}

Try it online.