Enumerating over generic and non-generic enumerators in C#

Foo.cs

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

public class Foo : IEnumerable<int>
{
    public IEnumerator<int> GetEnumerator()
    {
        yield return 42;
        yield return 1337;
    }

    IEnumerator IEnumerable.GetEnumerator()
    {
        throw new NotImplementedException();
    }
}

FooTests.cs

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

public class FooTests
{
    [Fact]
    public void ForEachWorks()
    {
        var results = new List<int>();
        foreach (var i in new Foo())
            results.Add(i);
        Assert.Equal(new List<int> { 42, 1337 }, results);
    }

    [Fact]
    public void ForEachOnUngenericThrows()
    {
        var results = new List<object>();
        Assert.Throws<NotImplementedException>(() =>
        {
            foreach (var x in (System.Collections.IEnumerable)(new Foo()))
                results.Add(x);
        });
    }
}

Both tests pass:

2 passed, 0 failed, 0 skipped, took 0,63 seconds (xUnit.net 2.3.1 build 3858).