Problem Description

“The game of yahtzee is a simple dice game. Each round, each player rolls five six sided dice. The player may choose to reroll some or all of the dice up to three times (including the original roll). The player then places the roll at a category, such as ones, twos, sixes, pair, two pairs etc. If the roll is compatible with the score, the player gets a score for this roll according to the rules. If the roll is not compatible, the player gets a score of zero for this roll.

The kata consists of creating the rules to score a roll in any of a predefined category. Given a roll and a category, the final solution should output the score for this roll placed in this category.”

[codingdojo.org]

Category 1 – Ones, Twos, Threes, Fours, Fives, Sixes

“Ones, Twos, Threes, Fours, Fives, Sixes: The player scores the sum of the dice that reads one, two, three, four, five or six, respectively. For example, 1, 1, 2, 4, 4 placed on "fours" gives 8 points.”

After reading this category description we could come up with the following spec:

Since we really want to implement six different categories we should also add some more scenarios like this one:

Now we have some specs but they will all fail since we don’t have anything implemented yet. So we have to come up with a model of dice rolls and categories. As the specs suggests we model the dice roll as a tuple of ints and the category as a discriminated union:

The tuple is a natural choice for the dice roll, but for easier calculation we add a helper function which converts it into a list. This allows use to use the standard list functions and therefore summing the values becomes trivial:

Now we can run our scenarios with any NUnit runner. I’m using the default NUnit GUI runner here, which gives me a picture like this:

Category 2 – Pair

“Pair: The player scores the sum of the two highest matching dice. For example, 3, 3, 3, 4, 4 placed on "pair" gives 8.”

The kata description gives us some new scenarios. As seen above we should specify them before writing the code.

Since we use a new category we now have to extend our model and the calcValue function:

Category 3 – Two pairs

“Two pairs: If there are two pairs of dice with the same number, the player scores the sum of these dice. If not, the player scores 0. For example, 1, 1, 2, 3, 3 placed on "two pairs" gives 8.”

Implementing this category is a little bit tricky but with the help of our Pair function and some more standard sequence combinators we can get our spec green:

Category 4 – Three of a kind

“Three of a kind: If there are three dice with the same number, the player scores the sum of these dice. Otherwise, the player scores 0. For example, 3, 3, 3, 4, 5 places on "three of a kind" gives 9.”

Now it is time to refactor our code. The sumAsPair function should be extended to a sumAsTuple function:

Category 5 – Four of a kind

“Four of a kind: If there are four dice with the same number, the player scores the sum of these dice. Otherwise, the player scores 0. For example, 2, 2, 2, 2, 5 places on "four of a kind" gives 8.”

With the help of the takeBestTuple function this becomes trivial:

type Category =

| Ones

  // …

| FourOfAKind

let calcValue category roll =

      // …

    | FourOfAKind  -> takeBestTuple 4 list

Category 6 – Small straight

“Small straight: If the dice read 1,2,3,4,5, the player scores 15 (the sum of all the dice), otherwise 0.”

As in all the above scenarios we don’t assume any specific order in our rolls but for this category it is easier to test if the data is sorted:

Category 7 – Large straight

“Large straight: If the dice read 2,3,4,5,6, the player scores 20 (the sum of all the dice), otherwise 0.”

Of course the implementation is exactly the same as for the small straight:

Category 8 – Full house

“Full house: If the dice are two of a kind and three of a kind, the player scores the sum of all the dice. For example, 1,1,2,2,2 placed on "full house" gives 8. 4,4,4,4,4 is not "full house".”

Implementing the FullHouse category is easy if we reuse our solutions to the Two pairs category:

Category 9 – Yahtzee

“Yahtzee: If all dice are the have the same number, the player scores 50 points, otherwise 0.”

Here we can use NaturalSpec’s ScenarioTemplates in order to specify all Yahtzees:

The implementation is pretty easy:

Category 10 – Chance

“Chance: The player gets the sum of all dice, no matter what they read.”

This seems to be the easiest category as we only have to sum the values:

Conclusion

We used a lot of F#’s sequence combinators, pattern matching and discriminated unions in this kata. I think this shows that F# is very well suited for such a problem and with NaturalSpec we can easily use a TDD/BDD approach.

The complete source code can be found in the NaturalSpec repository.

If you want to know more about a specific part of the kata or NaturalSpec feel free to contact me.

©2010 Rash thoughts about .NET, C#, F# and Dynamics NAV.. All Rights Reserved.

Fake – F# Make version 1.0.0

"FAKE – F# Make" is a build automation system, which is intended to provide a much better tooling support than XML-based build languages like MSBuild or NAnt. Due to its integration in F#, all benefits of the .NET Framework and functional programming can be used, including the extensive class library, powerful debuggers and integrated development environments like Visual Studio 2008, Visual Studio 2010 or SharpDevelop, which provide syntax highlighting and code completion.

Like F# itself the new build language was designed to be succinct, typed, declarative, extensible and easy to use.

• Project page with samples and articles
• Download page
• Github repository

NaturalSpec version 1.0.0

NaturalSpec is a UnitTest framework based on NUnit and completely written in F# – but you don’t have to learn F# to use it. The idea is that you can write your spec mostly in a natural language like in the following sample:

• Project page with samples and articles
• Download page
• Github repository

If you have any questions about the projects feel free to contact me.

©2010 Rash thoughts about .NET, C#, F# and Dynamics NAV.. All Rights Reserved.

1. Choosing an IDE

The first step is to choose an integrated development environment for NaturalSpec. At the current project status you should be able to use NaturalSpec with Visual Studio 2008, Visual Studio 2010 beta 2, the freely available Visual Studio 2008 Shell or the free IDE SharpDevelop 3.0.

2. Installing the testing framework

As NaturalSpec uses NUnit as the underlying testing framework we have to install NUnit 2.5. I also recommend installing TestDriven.Net in order to get a Unit Test runner within Visual Studio.

3. Installing F#

NaturalSpec is completely written in F# and all specs will also be written in F#. This doesn’t imply you have to learn programming in F# but we need the F# compiler to get things working. You can download the F# October 2009 CTP from the Microsoft F# Developer Center.

4. Downloading the latest version of NaturalSpec

You can download a .zip with the latest NaturalSpec libraries from GoogleCode.

5. Creating a spec

This part is written for using Visual Studio 2008. If you use SharpDevelop or Visual Studio 2008 Shell this might differ in some detail.

Start Visual Studio 2008 and create a new F# class library.

Rename Module1.fs in ListSpec.fs and delete script.fsx from the project:

Create a folder “Lib” and unzip the NaturalSpec libraries into it.

Add NaturalSpec.dll and nunit.framework.dll as references to your project:

Copy the following code into ListSpec.fs:

module ListSpec

open NaturalSpec

[<Scenario>]
let When_removing_an_3_from_a_small_list_it_should_not_contain_3() =
  Given [1;2;3;4;5]
    |> When removing 3
    |> It shouldn't contain 3
    |> Verify

If you have TestDriven.Net installed you can run your spec via right click in the solution explorer:

If you don’t like the TestDriven.Net test runner you might want to use the NUnit GUI runner. The output should look like:

In addition the test runner should produce a Spec output file with the name “Spec.txt” within the same folder.

Summary

In a minimal environment you need SharpDevelop, the F# compiler, NUnit and the NaturalSpec libraries for using NaturalSpec.

In the next post I will show how you can use NaturalSpec to create a spec for C# projects.

©2010 Rash thoughts about .NET, C#, F# and Dynamics NAV.. All Rights Reserved.

First of all we define a scenario for sorting:

/// predefined sorting scenario
let sortingScenario f list =
  Given list
    |> When sorting_with f
    |> It should be sorted
    |> It should contain_all_elements_from list
    |> It should contain_no_other_elements_than list

/// predefined Quicksort scenario
let quicksortScenario list = sortingScenario QuickSort list

Now we define some concrete test cases:

[<Scenario>]
let When_sorting_empty_list() =
  quicksortScenario []
    |> Verify

[<Scenario>]
let When_sorting_small_list() =
  quicksortScenario [2;1;8;15;5;22]
    |> Verify      

[<ScenarioTemplate(100)>]
[<ScenarioTemplate(1000)>]
[<ScenarioTemplate(2500)>]
let When_sorting_ordered_list n =
  quicksortScenario [1..n]
    |> Verify  

[<ScenarioTemplate(100)>]
[<ScenarioTemplate(1000)>]
[<ScenarioTemplate(2500)>]
let When_sorting_random_list n =
  quicksortScenario (list_of_random_ints n)
    |> Verify  

After we defined our spec the task is now to implement the sorting function. I am using a very short (and very naïve) Quicksort implementation in F#:

/// naive implementation of QuickSort - don't use it
let rec quicksort = function
  | [] -> []
  | pivot :: rest ->
     let small,big = List.partition ((>) pivot) rest
     quicksort small @ [pivot] @ quicksort big

let QuickSort x =
  printMethod ""
  quicksort x   

If we run the scenario, we get the following output (I shortened a bit):

Scenario: When sorting empty list

- Given []
– When sorting with QuickSort
=> It should be sorted
=> It should contain all elements from []
=> It should contain no other elements than []
==> Result is: []
==> OK
==> Time: 0.0355s

Scenario: When sorting small list

- Given [2; 1; 8; 15; 5; 22]
– When sorting with QuickSort
=> It should be sorted
=> It should contain all elements from [2; 1; 8; 15; 5; 22]
=> It should contain no other elements than [2; 1; 8; 15; 5; 22]
==> Result is: [1; 2; 5; 8; 15; 22]
==> OK
==> Time: 0.0065s

Scenario: When sorting ordered list

[…]  100 elements
==> OK
==> Time: 0.0939s

Scenario: When sorting ordered list

[…]  1000 elements
==> OK
==> Time: 0.7130s

Scenario: When sorting ordered list

[…]  2500 elements
==> OK
==> Time: 3.0631s

Scenario: When sorting random list

[…]  100 elements
==> OK
==> Time: 0.0485s

Scenario: When sorting random list

[…]  1000 elements
==> OK
==> Time: 0.1878s

Scenario: When sorting random list

[…]  1000 elements
==> OK
==> Time: 0.8713s

As you can see the function is much faster if we sort a random list. This is because of the naïve choice of the pivot element.

I don’t want to give better implementations here (use LINQ or PLINQ). I just wanted to show how we can easily verify a test function with NaturalSpec.

©2010 Rash thoughts about .NET, C#, F# and Dynamics NAV.. All Rights Reserved.

1. Using predefined scenarios

By writing predefined parameterized scenarios we can easily create a scenario suite with lots of different test cases:

// predefined scenario
let factorialScenario x result =
  Given x
    |> When calculating factorial
    |> It should equal result

[<Scenario>]
let When_calculation_factorial_of_1() =
  factorialScenario 1 1
    |> Verify   

[<Scenario>]
let When_calculation_factorial_of_10() =
  factorialScenario 10 3628800
    |> Verify

If we run these scenarios with NUnit we will get the following output:

Scenario: When calculation factorial of 1

  – Given 1

    – When calculating factorial

       => It should equal 1

==> OK

==> Time: 0.0093s

Scenario: When calculation factorial of 10

  – Given 10

    – When calculating factorial

       => It should equal 3628800

==> OK

==> Time: 0.0018s

2. Using the ScenarioTemplate attribute

The second and shorter option is to use the ScenarioTemplate attribute, which is inherited from NUnit’s new TestCase attribute:

// with ScenarioTemplate Attribute
[<ScenarioTemplate(1, 1)>]
[<ScenarioTemplate(2, 2)>]
[<ScenarioTemplate(5, 120)>]
[<ScenarioTemplate(10, 3628800)>]
let When_calculating_fac_(x,result) =
  Given x
    |> When calculating factorial
    |> It should equal result
    |> Verify

This code will create 4 different scenarios, which NUnit will display and report separately:

3. Using ScenarioSource

The third option is to use the ScenarioSource attribute. Here we define a function which generates TestData:

/// with a scenario source
let MyTestCases =
  TestWith 12 3 4
    |> And 12 4 3
    |> And 12 6 2
    |> And 1200 40 30
    |> And 0 0 0 |> ShouldFailWith (typeof<System.DivideByZeroException>)

And then we have to tell NaturalSpec which TestData a scenario should use:

[<Scenario>]
[<ScenarioSource "MyTestCases">]
let When_dividing a b result =
 Given a
   |> When dividing_by b
   |> It should equal result
   |> Verify

Summary

Sometime it makes sense to test a scenario with a bunch of different parameters. We can use the ScenarioTemplate attribute to easily parameterize our scenarios. If we want more flexibility we can use predefined scenarios with custom parameters or the ScenarioSource attribute.

©2010 Rash thoughts about .NET, C#, F# and Dynamics NAV.. All Rights Reserved.

Mocking objects is an important technique in Test-driven development (TDD) and allows us to simulate complex behavior.

“If an object has any of the following characteristics, it may be useful to use a mock object in its place:

• supplies non-deterministic results (e.g. the current time or the current temperature);
• has states that are difficult to create or reproduce (e.g. a network error);
• is slow (e.g. a complete database, which would have to be initialized before the test);
• does not yet exist or may change behavior;
• would have to include information and methods exclusively for testing purposes (and not for its actual task).”

Wikipedia

In our sample we want to mock the Dealer.SellCar() functionality. The first step is to create an C#-Interface for the Dealer:

namespace CarSellingLib
{
    public interface IDealer
    {
        Car SellCar(int amount);
    }
}

NaturalSpec is using Rhino.Mocks as the underlying mocking framework, so we have to create a reference to Rhino.Mocks.dll in our spec library.

Now we can modify our spec to:

// 1. open module
module CarSpec

// 2. open NaturalSpec-Namespace
open NaturalSpec

// 3. open project namespace
open CarSellingLib

// define reusable values
let DreamCar = new Car(CarType.BMW, 200)
let LameCar = new Car(CarType.Fiat, 45)

// 4. define a mock object and give it a name
let Bert = mock<IDealer> "Bert"

// 5. create a method in BDD-style
let selling_a_car_for amount (dealer:IDealer) =
  printMethod amount
  dealer.SellCar amount

// 6. create a scenario
[<Scenario>]
let When_selling_a_car_for_30000_it_should_equal_the_DreamCar_mocked() =
  As Bert
    |> Mock Bert.SellCar 30000 DreamCar  // 7. register mocked call
    |> When selling_a_car_for 30000
    |> It should equal DreamCar
    |> It shouldn't equal LameCar
    |> Verify

As you can see we changed part 4 (in order to get a mocked IDealer instead of the concrete Dealer). In part 7 we register our mocked behavior. We want that whenever Bert.SellCar is called with parameter 30000 the DreamCar should be returned.

The Verify-function checks if the mocked function has been called. If not the scenario will fail.

If we verify our spec with a NUnit runner we get the following output:

Scenario: When selling a car for 30000 it should equal the DreamCar mocked

- As Bert

- With Mocking

- When selling a car for 30000

=> It should equal BMW (200 HP)

=> It should not equal Fiat (45 HP)

==> OK

©2010 Rash thoughts about .NET, C#, F# and Dynamics NAV.. All Rights Reserved.

Like the TDD principle “Write the tests first” we should write our spec first and use the “Red-Green-Refactor” method.

"Red" – Create a spec scenario that fails

At first I created a F# class library project called “Spec.CarSelling” and added project references to NaturalSpec.dll and nunit.framework.dll (see “Getting started” for further explanations).

Now I can write my first scenario:

// 1. define the module
module CarSpec

// 2. open the NaturalSpec namespace
open NaturalSpec

// 3. open project namespace
open CarSellingLib

// 4. define a test context
let Bert = new Dealer("Bert")

// 5. create a method in BDD-style
let selling_a_car_for amount (dealer:Dealer) =
  printMethod amount
  dealer.SellCar amount

// 6. create a scenario
[<Scenario>]
let When_selling_a_car_for_30000_it_should_equal_my_DreamCar() =
  As Bert
    |> When selling_a_car_for 30000
    |> It should equal (new Car(CarType.BMW, 200))
    |> Verify

At this stage the scenario is ready but doesn’t compile. This means we are ready with the "Red"-stage.

"Green" – Make the test the pass

In order to get the test green we have to create a C# class library called CarSellingLib and define the enum CarType and the classes Dealer and Car. Sticking to the YAGNI-principle we implement only the minimum to get the spec green (and ToString()-members for the output functionality).

namespace CarSellingLib
{
    public enum CarType
    {
        BMW
    }
}

namespace CarSellingLib
{
    public class Car
    {
        public Car(CarType type, int horsePower)
        {
            Type = type;
            HorsePower = horsePower;
        }

        public CarType Type { get; set; }
        public int HorsePower { get; set; }

        public override string ToString()
        {
            return string.Format("{0} ({1} HP)", Type, HorsePower);
        }

        public override bool Equals(object obj)
        {
            var y = obj as Car;
            if(y == null) return false;
            return Type == y.Type && HorsePower == y.HorsePower;
        }
    }
}

using System;

namespace CarSellingLib
{
    public class Dealer
    {
        public Dealer(string name)
        {
            Name = name;
        }

        public string Name { get; set; }

        public Car SellCar(int amount)
        {
            return new Car(CarType.BMW, 200);
        }

        public override string ToString()
        {
            return Name;
        }
    }
}

When we add a project reference to our spec-project the UnitTests should pass and we have completed the "Green" step. (See "Getting started" if you don’t know how to run the spec.) Now we can add some more scenarios to our spec:

// 1. define the module 
module CarSpec

// 2. open NaturalSpec-Namespace
open NaturalSpec

// 3. open project namespace
open CarSellingLib

// 4. define a test context
let Bert = new Dealer("Bert")

// define reusable values
let DreamCar = new Car(CarType.BMW, 200)
let LameCar = new Car(CarType.Fiat, 45)

// 5. create a method in BDD-style
let selling_a_car_for amount (dealer:Dealer) =
  printMethod amount
  dealer.SellCar amount

// 6. create a scenario
[<Scenario>]
let When_selling_a_car_for_30000_it_should_equal_the_DreamCar() =
  As Bert
    |> When selling_a_car_for 30000
    |> It should equal DreamCar
    |> It shouldn't equal LameCar
    |> Verify      

[<Scenario>]
let When_selling_a_car_for_19000_it_should_equal_the_LameCar() =
  As Bert
    |> When selling_a_car_for 19000
    |> It should equal LameCar
    |> It shouldn't equal DreamCar
    |> Verify

// create a scenario that expects an error
[<Scenario>]
[<Fails_with "Need more money">]
let When_selling_a_car_for_1000_it_should_fail_with_Need_More_Money() =
  As Bert
    |> When selling_a_car_for 1000
    |> Verify

Now we are in the “Red”-Phase again.

"Refactor" – rearrange your code to eliminate duplication and follow patterns

After making the spec "Green" and doing some refactoring the project code could look like this:

namespace CarSellingLib
{
    public enum CarType
    {
        Fiat,
        BMW
    }
}

namespace CarSellingLib
{
    public class Car
    {
        public Car(CarType type, int horsePower)
        {
            Type = type;
            HorsePower = horsePower;
        }

        public CarType Type { get; set; }
        public int HorsePower { get; set; }

        # region ToString, Equals 

        public override string ToString()
        {
            return string.Format("{0} ({1} HP)", Type, HorsePower);
        }

        public override bool Equals(object obj)
        {
            var y = obj as Car;
            if(y == null) return false;
            return Type == y.Type && HorsePower == y.HorsePower;
        }

        #endregion
    }
}

using System;

namespace CarSellingLib
{
    public class Dealer
    {
        public Dealer(string name)
        {
            Name = name;
        }

        public string Name { get; set; }

        public Car SellCar(int amount)
        {
            if (amount > 20000)
                return new Car(CarType.BMW, 200);

            if (amount > 3000)
                return new Car(CarType.Fiat, 45);

            throw new Exception("Need more money");
        }

        public override string ToString()
        {
            return Name;
        }
    }
}

The spec output should look like the following:

Scenario: When selling a car for 1000 it should fail with Need More Money

- Should fail…
– As Bert
– When selling a car for 1000

Scenario: When selling a car for 19000 it should equal the LameCar

- As Bert
– When selling a car for 19000
=> It should equal Fiat (45 HP)
=> It should not equal BMW (200 HP)
==> OK

Scenario: When selling a car for 30000 it should equal my DreamCar

- As Bert
– When selling a car for 30000
=> It should equal BMW (200 HP)
==> OK

Scenario: When selling a car for 30000 it should equal the DreamCar

- As Bert
– When selling a car for 30000
=> It should equal BMW (200 HP)
=> It should not equal Fiat (45 HP)
>==> OK

4 passed, 0 failed, 0 skipped, took 1,81 seconds (NUnit 2.5).

Summary

I showed how we can use NaturalSpec for the Red-Green-Refactor process of C# projects and how easy it is to get a spec in natural language.

©2010 Rash thoughts about .NET, C#, F# and Dynamics NAV.. All Rights Reserved.

There are a lot of popular testing frameworks around which can be used for BDD including xUnit.net ,NUnit, StoryQ, MSpec, NSpec and NBehave. Most of them can be used with fluent interfaces and therefore provides a good readability of the sources. Some of them even provide the possibility to generate a spec in natural language out of passed Unit tests.

What is a spec?

“A specification is an explicit set of requirements to be satisfied by a material, product, or service.”

American Society for Testing and Materials (ASTM) definition

A spec is an important document for the communication process – it enables domain experts to communicate with developers. But how can you verify the compliance with the spec? The answer is: you have to write unit tests. Even with the mentioned frameworks there is a lot of work to do in order to translate a spec scenario into a Unit Test.

Question 7 in the famous Joel Test is “Do you have a spec?”.

The idea of NaturalSpec is to give domain experts the possibility to express their scenarios directly in compilable Unit Test scenarios by using a Domain-specific language (DSL) for Unit Tests. NaturalSpec is completely written in F# – but you don’t have to learn F# to use it. You don’t even have to learn programming at all.

Example 1 – Specifying a list

Let’s consider a small example. If we want to test a new List implementation a spec could look like this:

[<Scenario>]
let When_removing_an_3_from_a_small_list_it_should_not_contain_3() =
  Given [1;2;3;4;5]              // “Arrange” test context
    |> When removing 3           // “Act”
    |> It shouldn't contain 3    // “Assert”
    |> It should contain 4       // another assertion
    |> Verify                    // Verify scenario

I used BDD style here and expressed my scenario in a quite natural language. As the comments are indicating the scenario is following the Arrange Act Assert (“AAA”) pattern.

With the Keyword “Given” I can create a test context (the objects I want to test). In this sample I created a list with 5 elements. With the keyword “When” I call a function which does something with my test context. In this case I want to remove the value 3. In the Assert section (keywords “It should” or “It shouldn’t”) I can give some observations, which should hold for my manipulated test context.

When I run this scenario via a NUnit runner (i am using TestDriven.Net) I get the following output:

Scenario: When removing an 3 from a small list it should not contain 3

- Given [1; 2; 3; 4; 5]
– When removing 3
=> It should not contain 3
=> It should contain 4
==> OK

Example 2 – Specifying a factorial function

If you implement factorial function the spec could look like this:

[<Scenario>]
let When_calculating_fac_5_it_should_equal_120() =
  Given 5
    |> When calculating factorial
    |> It should equal 120
    |> Verify    

[<Scenario>]
let When_calculating_fac_1_it_should_equal_1() =
  Given 1
    |> When calculating factorial
    |> It should equal 1
    |> Verify          

[<Scenario>]
let When_calculating_fac_0_it_should_equal_0() =
  Given 0
    |> When calculating factorial
    |> It should equal 1
    |> Verify

And the output of NaturalSpec would look like this:

Scenario: When calculating fac 0 it should equal 0

- Given 0
– When calculating factorial
=> It should equal 1
==> OK

Scenario: When calculating fac 1 it should equal 1

- Given 1
– When calculating factorial
=> It should equal 1
==> OK

Scenario: When calculating fac 5 it should equal 120

- Given 5
– When calculating factorial
=> It should equal 120
==> OK

Getting started

Of course you can use NaturalSpec to specify C# objects. I see my post "Using NaturalSpec to create a spec for C# projects" for a small sample.

You can download NaturalSpec at GoogleCode and follow the “Getting started” tutorial in order to write your first automatically testable spec.

I am very interested in your feedback. Do you like the syntax? What should I change? Do you consider using a spec tool like NaturalSpec?

©2010 Rash thoughts about .NET, C#, F# and Dynamics NAV.. All Rights Reserved.