Rash thoughts about .NET, C#, F# and Dynamics NAV.

In my last two articles I gave an introduction in NaturalSpec and showed how to get started. This time I will show how we can use NaturalSpec to write automatically testable scenarios for C# projects.

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.

Test-Driven development (TDD) is a well known software development technique and follows the mantra “Red-Green-Refactor”. Behavior-Driven Development (BDD) is a response to TDD and introduces the idea of using natural language to express the Unit Test scenarios.

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?