test.cs

[Fact()]
public void getFizzBuzzTest()
{
    var mock = new Moq.Mock<Converter>();

    mock.Setup(c => c.convert(Moq.It.IsAny<int>()))
        .Returns((int val) => { return "" + val; });

    Play play = new Play(4, mock.Object);

    Assert.Equal("1, 2, 3, 4", play.getFizzBuzz());

    mock.Verify(c => c.convert(Moq.It.IsAny<int>()), Moq.Times.Exactly(4));
}