Pattern matching in c#

fizzbuzz.cs

using System.Collections.Generic;
using System.Linq;
using Microsoft.VisualStudio.TestTools.UnitTesting;
using Toopsie.Parsers;

namespace Toopsie.Specs
{
    [TestClass]
    public class PatternMatchFizzbuzz
    {
        PMatch fizzbuzz;

        static IEnumerable<int> Range(int from, int to)
        {
            for (var i = from; i <= to; i++)
                yield return i;
        }

        [TestInitialize]
        public void Setup()
        {
            fizzbuzz = new PMatch();
            fizzbuzz
                .When<int>(x => x % 15 == 0).Do(x => "fizzbuzz")
                .When<int>(x => x % 3 == 0).Do(x => "fizz")
                .When<int>(x => x % 5 == 0).Do(x => "buzz")
                .When<int>().Do(x => x)
                .When<IEnumerable<int>>().Do(x => from val in x select fizzbuzz.Invoke(x))
                .When<int, int>((from, to) => to >= from).Do((from, to) => fizzbuzz.Invoke(Range(from, to)))
                .When("fizzbuzz").Do(x => "Aha, you found the easter egg!");
        }

        [TestMethod]
        public void CurryFizzbuzz()
        {
            fizzbuzz.Invoke(3).ShouldBe("fizz");
            fizzbuzz.Invoke(4).ShouldBe(4);
            fizzbuzz.Invoke(45).ShouldBe("fizzbuzz");
            fizzbuzz.Invoke(1, 5).ToArray().ShouldBe(new object[] { "fizzbuzz", 2, "fizz", 4, "buzz" });
            fizzbuzz.Invoke("fizzbuzz").ShouldBe("Aha, you found the easter egg!");
        }
    }
}

It compiles, but the test fails ATM