I am reading "The Software Architect's Profession: An Introduction," by Marc T. Sewell and Laura M. Sewell. I am not writing a book review with this post. Instead, I would like to highlight some similarities between the two disciplines. Whether we are building with brick and mortar, wood, steel, or computer code, the roles and processes are analogous. The role of the architect is important for both, but when it comes to software, the architect often goes unfulfilled.

Compared to architecting and constructing homes, hospitals, and skyscrapers, architecting and developing software is new to many of us. In our minds, whether we understand the processes required to erect the Empire State building or not, most of us  possess an intuitive understanding of the distinct roles of the architect, scientist, engineer, builder, electrician, and plumber. We realize that buildings provide shelter, make our lives easier, and consist of rooms specific to living activities. We have living rooms, family rooms, meeting rooms, workout rooms, kitchens, ect. If we want to add on a garage, screened-in porch, or modify an existing room, the architect needs to plan for this in his/her design.

When it comes to software and the processes required to plan, design, develop, and test, many of us lack the intuitive knowledge of what is, or should be, necessary to build software. Just like a building, software makes our lives easier and consists of rooms, such as  chat rooms, document libraries, art studios, financial planning, shopping, and home buying to name a few. If we want to add on a new room or modify and existing, the architect needs to plan for this in his/her design.

It becomes easier to see how buildings and software are similar and how the roles specific to each appear to be obvious and necessary. A building needs an architect, a builder, an electrician, and so forth. Software, similarly, needs an architect, a developer, a tester, and so forth.

Ask yourself this, "how many buildings (homes, schools, hospitals, malls, ect.) can I think of that were built without an architect?" Hmmm... I probably cannot think of any, or I should hope the answer is zero.

Now ask yourself, "how many software applications were built without an architect?" This one I can answer more easily - several. I try to convince myself that so-and-so was "acting" as the architect on this or that project, but the nature of it is, too many software projects are built without a dedicated architect.

Why is it that we feel like a building requires an architect, but that software can get by without it?

Is it because over centuries and millennia, we have been exposed to the processes required to construct buildings on a daily basis? Whereas, since software is comparatively new, the processes and roles required are not fully defined, or engrained in us, or we have yet to see centuries worth of catastrophic errors from omitting these roles?

"Blaming software failure or difficulty on 'changing requirements' is merely symptomatic of the lack of true architecture." As owners and builders see what is being built, they realize what is incorrect and begin to make modifications to align their initial expectations with the reality before it is too late.

"It is equally erroneous to blame software failure on poor management. Even the best managers cannot produce a satisfying result from a bad design or a lack of design."

Without this post becoming tiresome and long-winded, this book draws some good comparisons between the nature of building structures and software and the roles necessary for each.

Do you have an architect in your organization? Is he/she only an architect, or is he/she sharing this responsibility? Why?

The marker interface is an interface that is empty. It does not implement any properties nor methods. It is used to mark the capability of a class as implementing a specific interface at run-time. In languages that do not provide support for associating metadata to a class, this approach can be useful. In C#, metadata attributes are available to apply to a class, and according to the .NET Framework 3.5 Design Guidelines for Developing Class Libraries, marker interfaces should be avoided.

When I first noticed these marker interfaces in project I immediately thought it was a code smell. It just did not seem "right." Why provide an interface that defines nothing? Why provide a marker interface that implements a non-marker interface? Obviously there must be a reason for this?

Two sources encourage me to avoid using marker interfaces and to use attributes in C#. Interface Design and .NET Type Design Guidelines - Interface Design.

There advice is to avoid this...

public interface IFooAssignable {}

public class FooAssignableAttribute : IFooAssignable

{

    // ...

}

And to embrace this approach...

[FooAssignable]

public class Foo

{

    // ...

}

public class FooAssignableAttribute : Attribute

{

    // ...

}

There appears to be more work involved in writing "good" code.

If I am using "marker" interfaces, I can do this...

if(foo is IFooAssignable)

{

    // ...

}

If I am using attributes, I can do something like this...

object[] attributes = foo.GetType().GetCustomAttributes(false);

foreach (string attribute in attributes)

{

    if(attribute == "FooAssignable")

    {

        // ...

    }

}

Or, thanks to Jarod Ferguson's suggestions on using extension methods and LINQ, I could have this...

public static class AttributeExtensions

{

    public static bool IsAttributedAs<T>(this object obj)

    {

        if(obj.GetType().GetCustomAttributes(false).Where(x => x is T).ToList().Count == 1)

            return true;

        return false;

    }

}

// Then wherever I want to check for the attribute marker...

if (foo.IsAttributedAs<FooAssignableAttribute>())

{

    // ...

}

At this point, while "marker" interfaces are a code smell to me, I am still on the fence when it comes to using them versus custom attributes. I will more than likely tend to favor the attribute approach, unless I can prove that the cost of reflection is too expensive for my situation. I admit, I will do what I can to omit marker interfaces, perhaps by using some other interface where possible.

What are you doing in situations like this? Can you offer me a more elegant solution?

I have been doing code reviews frequently this past week and have been remarking on the naming conventions of test methods. In a effort to try and find the rules of BDD naming conventions, I came across Dan North's introduction to BDD, which is a great starting point, and a blog post by David Laribee that has made a good impression on me. You can read up on BDD to learn more, this post will not go into detail about it.

From what I gathered from David Laribee's article, I like this. I REALLY like this.

By changing namespace, class, and method names, the behavior of each spec (test) is clearly revealed. In a larger suite of tests, if there are failures, I can more easily see what is failing and what trends, if any, are resulting in my failures. Before, I would name my test method names to describe a behavior, "Some concept should do this when given that." Getting the namespace and class name involved provides a more legible test result.

While reviewing a test case for a peer, I took this approach and arrived at the following scenario. I am changing the names of the methods to hide details. The original test method was "FilterToEndPointTestReport." Making this more readable, using my previous approach, we arrived at "FilterShouldUpdateStatusOnReportWhenDefaultFilterValueIsChanged." Great, that is better, but...

Applying the approach described in David's post, I now have this.

   1: namespace Specs_for_Filters

   2: {

   3:   public class When_default_filter_value_is_changed : FilterTestFixture

   4:   {

   5:     [Test]

   6:     public void Endpoint_should_be_updated_on_report {}

   7:     

   8:     [Test]

   9:     public void Endpoint_should_be_updated_on_grid {}

  10:     

  11:     [Test]

  12:     public void Endpoint_should_be_updated_on_chart {}

  13:   }

  14:   

  15:   public abstract class FilterTestFixture

  16:   {

  17:     // provide common functionality that will be used 

  18:     // among behavior-driven filter test classes.

  19:   }

  20: }

When my tests run, their resulting output is more legible. This approach helps me to think about my tests in terms of behavior rather than implementation. In my opinion, my test cases are now more abstract and more succinct.

I was in a design discussion today and mentioned the need for a singleton object in our solution. Further along in the discussion I was trying to find a word that describes the opposite of a singleton, but alas, I struggled to find a word that may or may not exist. I just referred to the inverse object as a "new object." As I pondered this later in the day, I considered adjectives describing the nature of objects. They can be many things, but two concepts that popped into my head to classify them were "complex" and "simple."

I started playing with the words and making them resemble singleton. "Complexton" did not sound right to me. I should mention that I was washing my hands as I was contemplating this. I lifted up my head, looked into the mirror, and thought, "SIMPLETON." The opposite of a singleton is a "simpleton."

If the opposite of a singleton is not a "simpleton," then what is it? Until I find a plausible answer, I will try and insert this new term into my next design discussion.

Duplicate code to me is wrong. Writing duplicate code to me is like using poor grammar. If I am unaware of it, I am none the wiser. However, if I knowingly use poor grammar or duplicate code, I feel bad.

After seeing too many duplications across methods in one or more classes, I decided to investigate a way to remove these. I am always looking to remove duplicate code, even code that shares similarities, I look to refator. Removing duplications is important to adapt more easily to change. When a code change is required, we should only have to make it in one place. The following article will show two relatively simple means to address this code smell, delegates and an Aspect-Oriented approach.

The example I am using in this article is seen below. It is a unit test class, StackFixture class, and it is extremely trivial. This is a typical unit test taken from Test-Driven Development in Microsoft .NET. I have added the logging functionality as an easy means to show how these types of DRY violations can occur. While the duplications in this example deal with logging, they could pertain to other, more complex, functionality as well. The approaches to removing duplications across methods in this article can work with these simple scenarios, as well as more complex ones.

Take for example this sample test case. Each test method logs a message before and after executing the test logic. This violates DRY. We want to keep our test logic in our method, but factor out the duplicate logging. Again, if we were not logging, but doing some repetitive logic, we could factor that out as well.

   1: [TestFixture]

   2: public class StackFixture : AbstractBaseFixture

   3: {

   4:     private Stack stack;

   5:  

   6:     [SetUp]

   7:     public void SetUp()

   8:     {

   9:         stack = new Stack();

  10:     }

  11:  

  12:     [Test]

  13:     public void Empty()

  14:     {

  15:         Log.Info("Starting Empty test");

  16:  

  17:         Assert.IsTrue(stack.IsEmpty);

  18:  

  19:         Log.Info("Ending Empty test");

  20:     }

  21:  

  22:     [Test]

  23:     public void PushOne()

  24:     {

  25:         Log.Info("Starting PushOne test");

  26:  

  27:         stack.Push("first element");

  28:         Assert.IsFalse(stack.IsEmpty, "After Push, IsEmpty should be false.");

  29:  

  30:         Log.Info("Ending PushOne test");

  31:     }

  32:  

  33:     [Test]

  34:     public void Pop()

  35:     {

  36:         Log.Info("Starting Pop test");

  37:  

  38:         stack.Push("first element");

  39:         stack.Pop();

  40:         Assert.IsTrue(stack.IsEmpty, "After Push - Pop, IsEmpty should be true.");

  41:  

  42:         Log.Info("Ending Pop test");

  43:     }

  44:  

  45:     [Test]

  46:     [ExpectedException(typeof(InvalidOperationException))]

  47:     public void PopEmptyStack()

  48:     {

  49:         Log.Info("Starting PopEmptyStack test");

  50:  

  51:         stack.Pop();

  52:  

  53:         Log.Info("Ending PopEmptyStack test");

  54:     }

  55: }

Remove Duplications with Delegates

Quite simply, we can remove our method duplications using a delegate, in this case, the System.Action delegate. Thanks to Ayende for helping me understand this option. We create a method, TestMethod (as shown below), and add it to our StackFixture class. The method takes two strings (string beforeMessage and string afterMessage) and the Action delegate, representing the test method logic. We will call this method within our test cases.

   1: public void TestMethod(string beforeMessage, string afterMessage, Action action)

   2: {

   3:     // before

   4:     Log.Info(beforeMessage);

   5:     

   6:     // invoke our method

   7:     action();

   8:     

   9:     // after

  10:     Log.Info(afterMessage);

  11: }

Then, in our tests, we replace the following test method...

   1: [Test]

   2: public void Pop()

   3: {

   4:     Log.Info("Starting Pop test");

   5:  

   6:     stack.Push("first element");

   7:     stack.Pop();

   8:     Assert.IsTrue(stack.IsEmpty, "After Push - Pop, IsEmpty should be true.");

   9:  

  10:     Log.Info("Ending Pop test");

  11: }

With the same method using our delegate approach.

   1: [Test]

   2: public void Pop()

   3: {

   4:     TestMethod("Starting Pop test", "Ending Pop test",

   5:                delegate

   6:                    {

   7:                        stack.Push("first element");

   8:                        stack.Pop();

   9:                        Assert.IsTrue(stack.IsEmpty, "After Push - Pop, IsEmpty should be true.");

  10:                    });

  11: }

We can replace each of our test methods with the same TestMethod using the System.Action delegate. It will then easy to omit our before and after strings replacing them with "action.Method.Name," or some other intelligent logic to determine what to log.

This approach works well, but delegates are often difficult to understand. If this solution suits your needs, make sure the implementation is easily maintainable. What is nice about this approach is how simple it is. There is no need to reference any assemblies outside of the .Net framework, i.e. no third party dependencies.

The Aspect-Oriented Approach

Aspect-Oriented Programming (AOP) is an entirely different animal. It certainly deserves more than just a blog post. Please read more about it online. This article will not explain the details of AOP.

If you are reading this, welcome back. I will assume you are now familiar with AOP. There are several options for AOP frameworks. Some frameworks I have used are Spring.net, Castle Project, and PostSharp. The former two provide IoC capabilities as well. I suggest using a well-supported framework, one with community support and frequent updates. Investigate for yourself, there are several nice options available.

AOP with Castle DynamicProxy

Hamilton Verissimo put together a good sample using Castle's DynamicProxy. It is a nice, clean implementation.This worked fine for me and would work well in other situations. However, in my scenario, if I were to use this approach, I needed to have each of my test classes extend from MarshalByRef. In addition, I would need to modify the underlying NUnit framework to create my proxies in order to provide advice. Since I could not do the latter, or did not want to investigate, I searched for other AOP options.

The DynamicProxy aproach to solving your AOP needs is a great option. It just did not work in my situation, only because NUnit executes each of my methods. I would need to somehow intercept the creation of my test class, create a proxy of it, and execute the test methods on it.

AOP with PostSharp

Gael Fraiteur's PostSharp is a great option for AOP needs. It is extremely clean and easy to use. It is the simplest AOP framework I have used. I suggest watching Gael's video tutorial.

The first thing I needed to do, besides downloading and installing PostSharp, is to add two references to my project, PostSharp.Laos and PostSharp.Public. After that, I create a simple class extending OnMethodInvocationAspect, called LoggingMethodInvocationAspect.

   1: [Serializable]

   2: public sealed class LoggingMethodInvocationAspect : OnMethodInvocationAspect

   3: {

   4:     private ILogger log;

   5:  

   6:     public LoggingMethodInvocationAspect(ILogger logger)

   7:     {

   8:         log = logger;

   9:     {

  10:  

  11:     public override void OnInvocation(MethodInvocationEventArgs eventArgs)

  12:     {

  13:         // before

  14:         log.Info("OnInvocation Before proceed");

  15:  

  16:         // invoke

  17:         eventArgs.Proceed();

  18:  

  19:         // after

  20:         log.Info("OnInvocation After proceed");

  21:     }

  22: }

At this point, all we need to do is apply our aspect on target methods. The "AttributeTargetMembers" attribute can use wildcards. This tells the AOP framework to only intercept those methods in the "MathService" class that start with "Test." Below is the sample where I specify the target assembly, target type (class or classes to intercept), and target methods to intercept. There are many features beyond what I am showing so do further investigation.

   1: [assembly: ClassLibrary.SampleInterfaces.LoggingMethodInvocationAspect(

   2:     AttributeTargetAssemblies = "ClassLibrary.UnitTesting.Sandbox",

   3:     AttributeTargetTypes = "ClassLibrary.UnitTesting.Sandbox.MathService", 

   4:     AttributeTargetMembers = "Test*")]

Finally, my StackFixture class now looks something like this. Notice that the duplicate logging logic is now removed and each test method is prefixed with "Test" in the method name. This is so that PostSharp can filter what methods to intercept.

   1: [assembly: ClassLibrary.SampleInterfaces.LoggingMethodInvocationAspect(

   2:   AttributeTargetAssemblies = "ClassLibrary.UnitTesting.Sandbox",

   3:   AttributeTargetTypes = "ClassLibrary.UnitTesting.Sandbox.MathService", 

   4:   AttributeTargetMembers = "Test*")]

   5:     

   6: [TestFixture]

   7: public class StackFixture

   8: {

   9:     private Stack stack;

  10: