IsAnagram.cs

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

public class Program
{
	public static void Main()
	{
		foreach (var test in GetTestCases())
		{
			var result = test.First.IsAnagram(test.Second);
			Console.WriteLine((result == test.Expected) ? "Success" : "FAIL");
		}
	}	
	
	public static IEnumerable<TestCase> GetTestCases()
	{
		yield return new TestCase { First = "add", Second = "dad", Expected = true };
		yield return new TestCase { First = "aad", Second = "dad", Expected = false };
		yield return new TestCase { First = "Astronomer", Second = "Moon starer", Expected = true };
		yield return new TestCase { First = "thorough", Second = "through", Expected = false };
		yield return new TestCase { First = "Jim Morrison", Second = "Mr. Mojo Risin'", Expected = true };
		yield return new TestCase { First = "123 Rook Street", Second = "999 Koro street", Expected = true };
	}
}

public static class StringExtensions
{
	public static bool IsAnagram(this string first, string second)
	{
		return first.Normalise().SequenceEqual(second.Normalise());
	}
	
	public static IEnumerable<char> Normalise(this string value)
	{
		if (value.Any(c => char.IsDigit(c)))
		{
			throw new ArgumentException("Digits are not permitted.", "value");
		}
		
		return value
			.ToLower()
			.Where(c => char.IsLetter(c))
			.OrderBy(c => c);
	}
}

public class TestCase
{
	public string First { get; set; }
	public string Second { get; set; }
	public bool Expected { get; set; }
}