using ls on the files to ensure that they're present.

simpletest2.cs

using System;
using System.Diagnostics;

public class simpletest
{
    static public void Main ()
    {
        Console.WriteLine(">>> use ls on the binary <<<");
        var psi = new ProcessStartInfo("/bin/ls", "-l /usr/bin/7z");
        var proc = new Process() { StartInfo = psi, };
        proc.Start();
        proc.WaitForExit();

        Console.WriteLine(">>> use ls on a missing file <<<");
        psi = new ProcessStartInfo("/bin/ls", "-l /usr/bin/7zzz");
        proc = new Process() { StartInfo = psi, };
        proc.Start();
        proc.WaitForExit();
    }
}