Collection Assertion in MSTest and Kata

I have been doing Prime Factor Kata with one of my friend. If you want to follow along, there is a great video post at Rickard Nilsson blog. For this Kata, my first attempt was to use C# (obviously), NUnit. All worked very well. So out of curiosity, I decided to change it a little bit, use MSTest. I was expecting the same code I wrote in NUnit would work in MSTest but to my surprise, even my first test failed. Here is my first test

Assert.AreEqual(1.Primes(), new List<int>());

Here is the Primes implementation

public static List<int> Primes(this int n)
{
   return new List<int>();
}

Very simple. In NUnit, when you assert a condition on a collection, it just does assertion, while in MSTest, you can not use Assert against a collection.If you need to do assert against a collection, you need to use CollectionAssert.AreEqual. So when I changed the code to CollectionAssert, it worked like a charm. But here is a catch though, if I had the code like

public static IList<int> Primes(this int n)

The assertion will not work since IList does not implement ICollection, rather it implements ICollection<T>. There are ways to work around that, but I found a better way of doing the whole thing anyway. If you want to do it like NUnit, then, what I would recommend is to install NBehave. Specifically the NBehave for .Net. With that installed, now the same test I used in the beginning of the blog would be like this and more readable.

1.Primes().ShouldBeEqualTo(new List<int>());

Which is more readable and the same code works with NUnit and MSTest. The whole benefit of Kata for me besides the obvious, I was able to compare little bit of MSTest and NUnit. Based on what I have done, I decided to use NUnit just for ‘Parameterized Test Fixtures’. One of the thing we do while doing the Kata is code, refactor. It turned out, all my tests were copy paste except the input and expected result.So rather than have eight separate tests now I have one consolidated test with the input and expected result been passed in as attribute to NUnit. Here is the final code

[TestCase(1, new int[0])]
[TestCase(2, new int[1] {2})]
[TestCase(3, new int[1] {3})]
[TestCase(4, new int[2] { 2, 2 })]
[TestCase(6, new int[2] { 2, 3 })]
[TestCase(8, new int[3] { 2, 2, 2 })]
[TestCase(9, new int[2] { 3, 3 })]
[TestCase(3*5*7*11, new int[4] {3,5,7,11})]
public void Should_Find_Primes(int t1, int[] t2)
{            
     Assert.AreEqual(t1.Primes(), t2);
}

Thats all about it, good way to start a new year by learning something new and cool.