https://github.com/codeyu/nanoid-net/blob/master/README.md

SidPocTest.cs

using System;
using System.Collections.Generic;
using System.Linq;
using Xunit;

public class SidPocTest
{
    private const int DefaultSize = 8;
        private const string DefaultAlphabet = "123456789abcdefghijkmnpqrstuvwxyzABCDEFGHJKLMNPQRSTUVWXYZ";

    [Fact]
    public void TestHasNoCollisions()
    {
        const int count = 10000 * 1000;
        var dictUsed = new Dictionary<string, bool>();
        foreach(var dummy in Enumerable.Range(1, count))
        {
            var result = Nanoid.Nanoid.Generate(DefaultAlphabet, DefaultSize);
            Assert.False(dictUsed.TryGetValue(result, out var _));
            dictUsed.Add(result, true);
        }
    }
}