We don’t have time for unit tests

This is probably one of the biggest bullsh*ts people usually tell in the world of software development:

unit-tests1

I’ve heard it many times before, and I bet you’ve heard it too. I was unfortunate enough to work for companies where PMs and other people had this mentality, even giving the impression that unit tests were a waste of time. “Just do it quick and dirty” – this was a very common sentence in one of the last companies I worked for.

A lot has been written about unit tests in the last 15 or 20 years, and the advantages should be obvious by now – you can refactor your code with confidence without the fear of breaking existing functionality, you can run unit tests as part of an automated build, and so on.

But there are disadvantages as well – you do need to spend some time to write the test and debug the piece of functionality you’re testing, as obvious. This is usually the excuse given for NOT writing unit tests. But the truth is that we need to test the functionality somehow – it’s not acceptable to write a piece of code without testing it, right? You simply have to test your code, one way or another – even if you don’t use unit tests.

That leaves me with another question – from a development perspective, do you think that the alternatives ways to test your code are faster than writing a unit test? I don’t think so. I still believe that unit testing is the fastest way to do it, if you have a decent enough experience with it (you don’t need to be an expert, though). Let’s analyse the following scenario below.

The scenario – discount calculator

Imagine that you are working on an e-commerce website – the UI is an ASP.NET website that uses a REST API (ASP.NET Web API), where all the business logic is. You need to implement a discount calculator in the API, based on the customer type:

  • Platinum (20% discount)
  • Gold (10% discount)
  • Silver (5% discount)
  • Standard (no discount)

Source code would be something like this:

public interface IDiscountCalculator
{
    decimal Calculate(decimal productPrice, CustomerType customerType);
}

public enum CustomerType
{
    Standard = 0,
    Silver = 1,
    Gold = 2,
    Platinum = 3
}

So let’s examine some of the different ways we could test the discount functionality.

1. Testing using the UI (website)

In this scenario you basically need to run the website and the API, and navigate to the page where the discount is being displayed (e.g. view shopping cart). This means that you might eventually need to login, search for a product, add it to the shopping cart and then view the shopping cart in order to check if the discount is correct or not. Also, you need to do it for each customer type.

As you can imagine, this is not the most efficient way to test this functionality. We need to compile and run both the website and the REST API (authenticate user, etc).

2. Testing the API using a REST client

This is more efficient compared to the previous example (testing the UI) because you can skip all the steps mentioned before and invoke the service using a REST client such as Postman or SoapUI. You still need to create sample HTTP requests that might include HTTP headers (content type, authorization, etc), HTTP method and message body (JSON request object).

Depending on the service, it might take a while to configure the requests for each customer type. Also, we need to compile and run the REST API. Remember that in this scenario all we want to do is to calculate the discount for each customer type.

3. Testing using a console application

This is one of the simplest ways to run the test. There’s no need to use the UI to get to the page where the discount is displayed and there’s no need to create HTTP requests in order to invoke the API, i.e. we can test directly the discount functionality using .NET code. Also, console applications are faster to compile and run compared to an ASP.NET website.

4. Testing using an unit test framework

It’s basically as simple and fast as creating a console application – just add add your unit tests to a class library and you’ll be able to run the tests in a few seconds, using Visual Studio built-in functionality or a tool such as Resharper.

Conclusion

Saying “we don’t have time for unit tests” is deceiving. Giving that we need to to test our code somehow, ask yourself if the alternative to unit tests is easier and/or faster (creating a sample console app to run some tests, etc) – I’m pretty sure that in most of the cases the unit testing is the better option.

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Code Kata – Numbers to Words, using javascript and TDD

This code kata is based on the KataNumbersInWords kata – convert numbers into words:

  • 3: “three”
  • 159: “one hundred and fifty-nine”
  • 2400: “two thousand and four hundred”

Katas are a good way to learn/practice TDD and/or learn more about a particular technology – in my particular case I decided to to this kata to improve my javascript skills.

The purpose of the exercise is to write the code incrementally, one step at a time – starting with the simplest case scenario (1 digit numbers) and then adding the code to handle the other scenarios (2 digit numbers, 3 digit numbers, etc).

Assume that the input is valid (number).

Test cases:

  • 1 digit numbers
    • 0 should return “zero”
    • 3 should return “three”
    • 7 should return “seven”
  • 2 digit numbers
    • 10 should return “ten”
    • 14 should return “fourteen”
    • 20 should return “twenty”
    • 21 should return “twenty-one”
    • 56 should return “fifty-six”
  • 3 digit numbers
    • 209 should return “two hundred and nine”
    • 300 should return “three hundred”
    • 417 should return “four hundred and seventeen”
    • 560 should return “five hundred and sixty”
    • 698 should return “six hundred and ninety-eight”
  • 4 digit numbers
    • 3004 should return “three thousand and four”
    • 4000 should return “four thousand”
    • 5020 should return “five thousand and twenty”
    • 6300 should return “six thousand and three hundred”
    • 7111 should return “seven thousand and one hundred and eleven”
  • 5 digit numbers
    • 40000 should return “forty thousand”
    • 70393 should return “seventy thousand and three hundred and ninety-three”
    • 87654 should return “eighty-seven thousand and six hundred and fifty-four”
  • 6 digit numbers
    • 500000 should return “five hundred thousand”
    • 803308 should return “eight hundred and three thousand and three hundred and eight”
    • 999999 should return “nine hundred and ninety-nine thousand and nine hundred and ninety-nine”

You can see my implementation here (I’m using WebStorm v8 and JS Test Driver):

Download the code (WebStorm project): NumbersToWords.zip

Improving LINQ code reusability: Select method

Select method is used to project each element of a sequence into a new form, i.e. it can be used to map a collection of one type to a collection of another type. In this article I’ll show you a simple approach that will allow you to reuse the code used in the Select method.

Table of contents

The Problem

Consider the following model:

Let’s suppose that you have a services layer, so you don’t want to expose your domain objects directly to the client applications. Instead you create a set of data contracts (or DTOs, if you prefer):

At some stage you’ll have to convert those Domain objects to data contracts. This is a common way of doing it:

var details = repository.All<Album>().Select(album => new AlbumDetail {
    AlbumId = album.AlbumId,
    Price = album.Price,
    Title = album.Title,

    ArtistId = album.ArtistId,
    GenreId = album.GenreId,
    ArtistName = (album.Artist == null) ? null : album.Artist.Name,
    GenreName = (album.Genre == null) ? null : album.Genre.Name
});

There is a problem with this approach – if you need to query the same collection but using different criteria you have to duplicate the code inside the Select method.

Solution 1 – Creating a method for the mapping

In order to reuse the code, we can create a method that converts Album objects (Domain) to data contract objects:

private static AlbumSummary CreateAlbumSummary(Album album)
{
    return new AlbumSummary {
        AlbumId = album.AlbumId,
        Title = album.Title,

        ArtistName = (album.Artist == null) ? null : album.Artist.Name
    };
}

private static AlbumDetail CreateAlbumDetail(Album album)
{
    return new AlbumDetail {
        AlbumId = album.AlbumId,
        Price = album.Price,
        Title = album.Title,

        ArtistId = album.ArtistId,
        GenreId = album.GenreId,
        ArtistName = (album.Artist == null) ? null : album.Artist.Name,
        GenreName = (album.Genre == null) ? null : album.Genre.Name
    };
}

Using the code:

var albums = Albums.Select(CreateAlbumDetail);
var albumsByGenre = Albums.Where(x => x.GenreId == genreId).Select(CreateAlbumDetail);

// alternative way
var albums2 = Albums.Select(x => CreateAlbumDetail(x));
var albumsByGenre2 = Albums.Where(x => x.GenreId == genreId).Select(x => CreateAlbumDetail(x));

Solution 2 – Creating a generic ObjectMapper object

The previous solution solves the code reusability problem, but there’s still a tight coupling between components. Abstractions should be used to implement loose coupling between components – in this case, to abstract the mapping code.

Step 1: define a contract (interface) with a method that converts one object of type TSource to an object of type TDestination:

public interface IObjectMapper
{
    TDestination Map<TSource, TDestination>(TSource source);
}

Step 2: create a class that implements IObjectMapper (click to expand):

public class ObjectMapper : IObjectMapper
{
    private Dictionary<Type, Func<object, object>> Mappers = new Dictionary<Type, Func<object, object>>
    {
        { typeof(Tuple<Album, AlbumDetail>), CreateAlbumDetail },
        { typeof(Tuple<Album, AlbumSummary>), CreateAlbumSummary }

        // more mappings here
        // ....
    };


    public TDestination Map<TSource, TDestination>(TSource source)
    {
        if(source == null)
            return default(TDestination);

        Func<object, object> mapper = null;
        Type key = typeof(Tuple<TSource, TDestination>);

        if(Mappers.TryGetValue(key, out mapper))
        {
            var newObject = mapper(source);
            return (TDestination) newObject;
        }

        string errorMessage = string.Format("Invalid mapping (Source: {0}, Destination: {1})";,
                                            typeof(TSource).FullName, 
                                            typeof(TDestination).FullName);
        
        throw new InvalidOperationException(errorMessage);
    }


    private static object CreateAlbumDetail(object source)
    {
        var album = source as Album;

        return new AlbumDetail {
            AlbumId = album.AlbumId,
            Price = album.Price,
            Title = album.Title,

            ArtistId = album.ArtistId,
            GenreId = album.GenreId,
            ArtistName = (album.Artist == null) ? null : album.Artist.Name,
            GenreName = (album.Genre == null) ? null : album.Genre.Name
        };
    }

    private static object CreateAlbumSummary(object source)
    {
        var album = source as Album;

        return new AlbumSummary {
            AlbumId = album.AlbumId,
            Title = album.Title,
            
            ArtistName = (album.Artist == null) ? null : album.Artist.Name
        };
    }
}

Example 1: Using LINQ

Using the mapper in a LINQ expression – convert an Album collection to an AlbumSummary collection:

IObjectMapper mapper = new ObjectMapper();

IEnumerable<AlbumSummary> summaries = repository.All<Album>()
                                        .Select(mapper.Map<Album, AlbumSummary>);

Example 1: Mapping a single object

Using the mapper for a single object:

var album = new Album {
    AlbumId = 1,
    Price = 10.0m,
    Title = "The Dreamer",
    Artist = new Artist { ArtistId = 1, Name = "José James" },
    Genre = new Genre { GenreId = 1, Name = "Jazz" }
};

IObjectMapper mapper = new ObjectMapper();

AlbumDetail albumDetail = mapper.Map<Album, AlbumDetail>(album);

Unit Testing

Some NUnit tests:

[Test]
public void Given_a_non_existing_mapping_when_mapping_object_then_should_throw_InvalidOperationException()
{
    // arrange
    IObjectMapper mapper = new ObjectMapper();
    var albumDetail = new AlbumDetail();

    // act/assert
    Assert.Throws<InvalidOperationException>(() => 
        // non-existing mapping
        mapper.Map<AlbumDetail, AlbumSummary>(albumDetail)
    );
}

[Test]
public void Given_an_album_when_mapping_to_album_summary_should_equals_expected_album_summary()
{
    // arrange
    IObjectMapper mapper = new ObjectMapper();
    
    var album = new Album {
        AlbumId = 4,
        Price = 10.0m,
        Title = "Heritage",
        Artist = new Artist { ArtistId = 4, Name = "Opeth" },
        Genre = new Genre { GenreId = 4, Name = "Metal" }
    };

    var expectedAlbumSummary = new AlbumSummary {
        AlbumId = 4,
        ArtistName = "Opeth",
        Title = "Heritage"
    };
    
    // act
    AlbumSummary albumSummary = mapper.Map<Album, AlbumSummary>(album);
    
    // assert
    Assert.AreEqual(albumSummary, expectedAlbumSummary);
}

Final thoughts

In this article you learned how to reuse the code used in the Select method, and how you can use that code to map single objects. But writing mapping code is tedious and time consuming. There are mapping tools out there that can make your life easier – AutoMapper is one of them. I’ve used it in the past and I definitely recommend it. So, why use Automapper? Quoting their website:

“What makes AutoMapper interesting is that it provides some interesting conventions to take the dirty work out of figuring out how to map type A to type B. As long as type B follows AutoMapper’s established convention, almost zero configuration is needed to map two types”

“Mapping code is boring. Testing mapping code is even more boring. AutoMapper provides simple configuration of types, as well as simple testing of mappings”

References

Downloads

Download the demo project (VS2010): LINQ-Select.zip

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