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Rickard blogs about creating software solutions using ASP.NET and agile practices.
TDD Katas has become very popular in a small segment of the development community and we call our selves software craftsmen. We are passionate about software development as a craft and engage in different activities to better our selves and our peers.
My first kata cast, for instance, has been viewed close to 10k times on Vimeo since its publication. Much of the attention is of course due to Roy Osherove linking to my blog post from his TDD Kata 1 page. This time Roy initiated a sequel, meant to introduce interaction based testing using mocks and possibly stubs, and continue the teaching process of TDD and unit testing practices.
The following screen cast covers the entire kata in .NET, complete with Osherove’s three steps as well as manual UI testing at the end.
For best viewing experience I recommend watching it on Vimeo.com in HD
String Calculator TDD Kata 2 - Interactions from Rickard Nilsson on Vimeo.
The tools I use are Visual Studio, ReSharper, TestDriven.NET, Moq for mocking, and NUnit.
The code and Visual Studio solution for the finished Kata can be downloaded from GitHub:
Download source
As Osherove mentions in his instructions, this kata is not as simple as the first part, nor as simple as most katas out there. The reason is the element of interaction based unit testing involved, which is quite difficult to wrap you mind around, and it took quite a while to get the steps right. I thought I should share my path to the kata in its present form for others to learn from and comment on.
Step 1. Everytime you call Add(string) it also outputs the number result of the calculation in a new line to the terminal or console. (remember to try and do this test first!)
As I did this test first I started out pretty much as how it ended up in the cast. However, after a while I tried to take a step back and see if there were any smells in the code I had not yet discovered.
I found that I didn’t really like the mixed responsibilities that the Calculator class got when I introduced writing to the console. This could be seen as a logging feature and thus a perfect candidate to become an aspect (in AOP). I started playing around with PostSharp and ended up with the following solution which is quite clean.
[Serializable] public class OutputAttribute : OnMethodBoundaryAspect { [NonSerialized] private IContainer container;
public override void OnExit(MethodExecutionArgs args) { var console = container.Resolve<IConsole>(); console.WriteLine(args.ReturnValue.ToString()); }
[OnDeserialized] public void OnDeserialized(StreamingContext context) { container = ContainerFactory.Current; } }
Which, at most, leaves the mark of a custom attribute in the Calculator class:
public class Calculator { [Output] public int Add(string value) { ... } }
The problem with this solution is the way PostSharp works. It does all its magic as a post compilation step so everything is pretty much static. This is a problem in a testing scenario when we need to inject the mocked console in this case, hence the smelly ContainerFactory.Current stuff.
Another problem with this solution is that in part three, the console app, we need to disable or override what is outputed. This ends up becoming a static mess which did not feel right at all. If you have another view on this please leave a comment.
Step 2. Create a program (test first)that uses string calculator, which the user can invoke through the terminal/console by calling “scalc ‘1,2,3’” and will output the following line before exiting: “The result is 6”
For step 2 and 3 I thought a bit about refactoring to a UI design pattern like MVP, MVC or MVVM but finally decided to drop it, mainly because I didn’t know any framework like that for console applications. If the application grows I think this is the right way to go, but for the known requirements it’s an overkill, especially considering how small the solution is.
Step 3. Instead of exiting after the first result, the program will ask the user for“another input please” and print the result of the new user input out as well, until the user gives no input and just presses enter. in that case it will exit.
I played around a bit with SpecFlow, which has ha free form Given/When/Then specification syntax, on the later part of the kata. However, I felt that I lost velocity so I dropped it as well. Maybe, if I had some way of conducting complete acceptance testing through a real console, I would have pursued this further. It was simply too much to write, for example:
Scenario: Prompt user for another input Given a new string calculator And the user has entered: a valid input When the program has outputed The result is 1 Then the user is prompted for another input Scenario: Quit on empty input Given a new string calculator And the user is prompted for another input When the user hits enter Then the program should exit
Scenario: Prompt user for another input
Given a new string calculator
And the user has entered: a valid input
When the program has outputed The result is 1
Then the user is prompted for another input
Scenario: Quit on empty input
And the user is prompted for another input
When the user hits enter
Then the program should exit
Figure 3. SpecFlow Feature specification for the console app If you have any thoughts, comments, suggestions, or any other feedback please leave them below or ping me on twitter.
Are you new to the concept of code katas? Read my previous blog post and watch me perform the String Calculator Kata.
In my never ending goal of self improvement in the techniques and tools I use I’ve been practicing a version of the Prime Factors Kata for a while.
The Prime Factors Kata, initially sparked by the infamous Uncle Bob Martin, is about finding an arbitrary number’s prime factors. In the cast I show how my TDD practice has evolved into a flavor of BDD, mainly to reduce duplication in the unit tests. I also show off the awesome power of my current toolset which includes the Visual Studio 2010 and the latest versions of ReSharper, TestDriven.NET, NUnit and NBehave.
Though my performance is not yet perfected I want to put it out there because I feel there are no C# version that can really match the Ruby version in elegance and wit. This is my attempt to show what you can do with the C# language when you know the frameworks really well.
Please leave comments and/or suggestions below or record your own kata session in response.
Prime Factors Kata in C# from Rickard Nilsson on Vimeo.
If you are new to the Prime Factors Kata, code katas in general, or TDD for that matter, you may find the steps I take unnecessary or weird. You may want to watch the annotated version in which Uncle Bob explains why each step is taken and why they are taken in that order.
Many have recorded there own versions of the Prime Factors Kata which all inspired me in the way I practice it. The cast that inspired me the most is
there are also a few other C# casts worth watching for comparison by:
After I posted my Code Kata Cast I received some feedback regarding the ReSharper templates I use to speed up my coding. I decided to share them with the public (like so many before me) in hope that others may benefit from them, as I do.
rickardn-resharper-templates.zip (1,44 kb)
After you’ve downloaded the zip-file and unpacked it, open Visual Studio and the ReSharper Templates Explorer: Menu –> ReSharper –> Live Templates…
Click on Import… as the screen shot below shows, and find the file “rickardn-resharper-live-templates.xml”
Then click the “File Templates” tab and repeat the procedure for the “rickardn-resharper-file-templates.xml” file.
Good luck with your katas!
Much of the legacy ASP.NET code I’ve seen is littered with calls to methods on the HttpServerUtility class,
Server.MapPath(…)
Why, if your suite has thousands of tests and many calls IO or datebases, the tests will run slowly, and the developers on the team won’t run them as often. Ultimately, you may loose your investment in automated testing because it isn’t providing the promised feedback.
If the code behind code calls Server.MapPath() it is actually calling the Server property on the Page base class which returns HttpContext.Current.Server. This is an instance of the HttpServerUtility class, which is sealed and thus pretty impossible to fake out*.
In the namespace System.Web.Abstractions, which is part of ASP.NET 3.5, lives an abstraction of the HttpServerUtility, called HttpServerUtilityBase. It has a concrete implementation named HttpServerUtilityWrapper that takes an HttpServerUtility instance as a constructor parameter, as follows:
public sealed class HttpServerUtility { // ... }
public abstract class HttpServerUtilityBase { // ... }
public class HttpServerUtilityWrapper : System.Web.HttpServerUtilityBase { public HttpServerUtilityWrapper(HttpServerUtility httpServerUtility) {} // ... }
By leveraging a simple form of dependency injection we can preserve the old code as a first step of refactoring, and using an overloaded constructor to inject the fake object in our unit test.
public class Presenter { private HttpServerUtilityBase Server; public Presenter(HttpServerUtilityBase httpServerUtility) { Server = httpServerUtility; } public Presenter() { Server = new HttpServerUtilityWrapper(HttpContext.Current.Server); } public void PageLoad() { var path = Server.MapPath(…) } }
Now, in a unit test for the Presenter class we can inject a fake server utility, which won’t call any IO.
[Test] public void PageLoad_WhenCalled_ExpectedBehavior() { var fakeServerUtility = new HttpServerUtilityFake(); // implemented in the test suite var presenter = new Presenter(fakeServerUtility); presenter.PageLoad(); // Assert expected behavior }
Instead of implementing your own fake you can easily use your preferred isolation (mocking) framework of choice.
The goal is to isolate the class under test from all of its dependencies, weather they call IO, a database, a third party component, or even statics or touch static state. The point is that we want to assert that the class under test behaves as expected, not how the underlying framework behaves.
By leveraging the System.Web.Abstractions namespace we can preserve much of the existing ASP.NET code while covering it with tests.
_________ * Unless using TypeMock Isolator