Did God use XP or Scrum?

I was wandering around my house in a sleepy haze this morning with thoughts gently pulsating into my peripheral consciousness. I switched on the light and said to myself "Let there be light, and there was light" and then two peripheral thoughts blurred into focus at once prompting me to rummage through my wife's academic books (she's a teacher of Religion) and read through the first chapter of the Jeudo-Christian Old Testament.

Jokes aside about developer's egos it is quite clear that God used iterative development (or creation). Give the first chapter of Genesis a read for the compelling evidence.

In fact I think there is a clear case for claiming God was a YAGNI type of mono-deity as he creates light on day one but doesn't introduce the Sun until day four (verse 16: "God made two great lights--the greater light to govern the day and the lesser light to govern the night.") and though I've personally never worked on a project of that scale I can safely guess that there was some serious refactoring going on there! This also shows that the Creator has a real talent for deciding what the next most important thing should be.

Some of the more observant out there may have noticed that God was also using a bit of Behaviour Driven Development but being God he uses "Let there be" rather than "Should" before each one of his tests.

You may be wary of reading quite so much into the text but I think it's safe to say there was no BUFD going and can you imagine it if there was: on the first day he drew up the requirements, on the second day he wrote the design document, on the third day he finally stared, on the fourth day he realised that he'd forgotten the light and had to submit a change request...

YAGNI battles the Black Swans

There's been a lot of fuss in the economic world about a book called The Black Swan: The Impact of the Highly Improbable by Allen Lane. Lane uses the metaphor of the discovery of the Black Swan to explain his theory: basically before the discovery of Australia people believed there were only white swans in the world and created a whole set of theories around this 'fact'. Then a black swan was discovered in Australia junking the theories.

Using this as a template Lane defines a Blank Swan as a highly improbable event with three principle characteristics: it is unpredictable; it carries a massive impact; and, after the fact, we concoct an explanation that makes it appear less random and more predictable than it was.

Lane goes onto criticize businesses, markets and politicians for their over confidence in prediction. Lane even goes to the extent to suggest that it is a cold, hard fact that we cannot predict Black Swans but by preempting the future based on our belief that only White Swans exist we set ourselves up for disaster. So when a Black Swan does come along - and Lane argues that they come up a lot more than we predict - we've made things a whole lot worse by planning around White Swans.

Any developer who's every used the phrase "You Ain't Gonna Need It" would identify with Lane's theory. YAGNI tell's us that we should only implement what we need not what we foresee we need - no matter how sure you are that you're gonna need it. By writing code which preempts the future design we are building systems for White Swans and when that Black Swan comes along (and it will) we're going to be running around trying to refactor a load of over-engineered code. The difference between a Black Swan developer and a White Swan developer is the Black Swan developer accepts this and uses YAGNI to battle it where as a White Swan developer just re-engineers his predictions by turning the latest Black Swan into another White Swan - that is until the next Black Swan rears it's ugly head.

I think YAGNI developers - either naturally or through experience - think that life is full of Black Swans. I think that this is why some developers don't get YAGNI: they only believe in white ones. Maybe a different approach is not to say to them "You ain't gonna need it" but maybe say "Black Swan".

Don't Expect too much

A long while ago (well over two years) there was a lot of fuss made on the testdrivendevelopment Yahoo group about having only one assertion per test. Dave Astels wrote a great little article and a little more fuss was made. It was one of those things you knew made sence but sounded a lot of work. I played with one assertion per test anyway and suddenly felt my code developing more fluidly as I focused on only one thing at a time and my tests looked clearer (more behavoir orientated) and refactoring became a lot simpler too.

Then Dave Astels came along and pushed the envelope further with One Expectation per Example. This really grabbed my attention as I had been enjoying the benefits of keeping my test code clean with one assertion per test but anything with mocks in it just turned into out of control beasts (especially some of the more complex logic such as MVP). Even simple four liners such as below would end up with four expectations:

public AddOrder(OrderDto)
{
Customer customer = session.GetCurrentCustomer();
customer.AddOrder(OrderFactory.CreateOrder(OrderDTO));

workspace.Save(customer);
}

Then everytime I needed to add new functionality I had to add more expectations and anyone who read the work (including myself after 24 hours) would struggle to make head or tale out of the monster. And if tests failed it would take a day to find which expectation went wrong. If you're not careful you end up with the TDD anti-pattern The Mockery.

I had read Dave Astels article several times but couldn't fathom out how it worked especially seeing it was written in Ruby with the behaviour driven RSpec. In the end I had to write it out into .NET myself before I got it.

So here is a break down of how I got Dave's One expectation per example to work for me:

One Expectation Per Example (C#)
One of the first things to note is Dave uses the builder pattern in his example. The idea is that the Address object interacts with a builder to pass it's data to rather than allowing objects to see it's state directly thus breaking encapsulation. I would like to go into this technique in more detail in another article but to deliver the point quickly think that you may create an HTML builder to display the address on the web.

Well let's start with Dave's first test:

[TestFixture]
public class OneExpectationPerExample
{
[Test]
public void ShouldCaptureStreetInformation()
{
    Address addr = Address.Parse("ADDR1$CITY IL 60563");

    Mockery mocks = new Mockery();
    IBuilder builder = mocks.NewMock<IBuilder>();

    Expect.Once.On(builder).SetProperty("Address1").To("ADDR1");

    addr.Use(builder);

    mocks.VerifyAllExpectationsHaveBeenMet();
}
}

You may have noticed that I've changed a few things maily to make it look consistant with .NET design practices. Basically I've introduced a Parse method rather than the from_string method Dave uses.

Now we need to get this baby to compile. First we need to create the Address class like so:

public class Address
{
public static Address Parse(string address)
{
  throw new NotImplementedExpection();
}

public void Use(IBuilder builder)
{
  throw new NotImplementedExpection();
}
}

And the IBuilder interface:

public interface IBuilder {}

Now it compiles but when we run it we get the following:

   mock object builder does not have a setter for property Address1

So we need to add the Address1 property to the IBuilder. Then we run and we get:

    TestCase 'OneExpectationPerExample.ShouldCaptureStreetInformation'
failed: NMock2.Internal.ExpectationException : not all expected invocations were performed
Expected:
1 time: builder.Address1 = (equal to "ADDR1") [called 0 times]

Let's implement some working code then:

public class Address
{
private readonly string address1;

private Address(string address1)
{
  this.address1 = address1;
}

public static Address Parse(string address)
{
    string[] splitAddress = address.Split('$');

    return new Address(splitAddress[0]);
}

public void Use(IBuilder builder)
{
    builder.Address1 = address1;
}
}

Run the tests again and they work! So let's move onto the second part of implementing the Csp. Here's the new test:

[Test]
public void ShouldCaptureCspInformation()
{
    Address addr = Address.Parse("ADDR1$CITY IL 60563");

    Mockery mocks = new Mockery();
    IBuilder builder = mocks.NewMock<IBuilder%gt;();

    Expect.Once.On(builder).SetProperty("Csp").To("CITY IL 60563");

    addr.Use(builder);

    mocks.VerifyAllExpectationsHaveBeenMet();
}

Now a little refactoring to get rid off our repeated code we turn it into this:

[TestFixture]
public class OneExpectationPerExample
{
private IBuilder builder;
private Address addr;
private Mockery mocks;

[SetUp]
public void SetUp()
{
    mocks = new Mockery();

    builder = mocks.NewMock<ibuilder>();

    addr = Address.Parse("ADDR1$CITY IL 60563");
}

[TearDown]
public void TearDown()
{
mocks.VerifyAllExpectationsHaveBeenMet();
}

[Test]
public void ShouldCaptureStreetInformation()
{
    Expect.Once.On(builder).SetProperty("Address1").To("ADDR1");

    addr.Use(builder);
}

[Test]
public void ShouldCaptureCspInformation()
{
    Expect.Once.On(builder).SetProperty("Csp").To("CITY IL 60563");

    addr.Use(builder);
}
}

Looking good! We run the new test and we get the usual error for having no Csp property on the IBuilder so we add that:

public interface IBuilder
{
string Address1 { set; }
string Csp { set; }
}

Then we run the test again and we get:

   TestCase 'OneExpectationPerExample.ShouldCaptureCspInformation'
failed: NMock2.Internal.ExpectationException : unexpected invocation of builder.Address1 = "ADDR1"
Expected:
1 time: builder.Csp = (equal to "CITY IL 60563") [called 0 times]

Oh no. This is where Dave's article falls apart for .NET.
Basically RSpec has an option to create Quite Mocks which quitely ignore any unexpected calls. Unfortunately I know of no .NET mock libaries that have such behaviour (though I have since been reliably informed by John Donaldson on the tdd yahoo group that it is possible with the NUnit mock library) . Though there is a way out: stub the whole thing out by using Method(Is.Anything):

[Test]
public void ShouldCaptureCspInformation()
{
Expect.Once.On(builder).SetProperty("Csp").To("CITY IL 60563");

// stub it as we're not interested in any other calls.
Stub.On(builder).Method(Is.Anything);

addr.Use(builder);
}

Just be careful to put the Stub AFTER the Expect and not before as NMock will use the Stub rather than the Expect and your test will keep failing.

So now we run the tests and we get:

   TestCase 'OneExpectationPerExample.ShouldCaptureCspInformation'
failed:
TearDown : System.Reflection.TargetInvocationException : Exception has been thrown by the target of an invocation.
----> NMock2.Internal.ExpectationException : not all expected invocations were performed
Expected:
1 time: builder.Csp = (equal to "CITY IL 60563") [called 0 times]

Excellent NMock is now behaving correctly we can finish implementing the code:

public class Address
{
private readonly string address1;
private readonly string csp;

private Address(string address1, string csp)
{
    this.address1 = address1;
    this.csp = csp;
}

public static Address Parse(string address)
{
    string[] splitAddress = address.Split('$');

    return new Address(splitAddress[0], splitAddress[1]);
}

public void Use(IBuilder builder)
{
    builder.Address1 = address1;
    builder.Csp = csp;
}
}

Run the test and it works! Now if we run the whole fixture we get:

   TestCase 'OneExpectationPerExample.ShouldCaptureStreetInformation'
failed: NMock2.Internal.ExpectationException : unexpected invocation of builder.Csp = "CITY IL 60563"

All we need to do do is go back and add the Stub code to the street test. That's a bit of a bummer but we could refactor our tests to do the call in the tear down like so:

[TearDown]
public void UseTheBuilder()
{
Stub.On(builder).Method(Is.Anything);

addr.Use(builder);

mocks.VerifyAllExpectationsHaveBeenMet();
}

[Test]
public void ShouldCaptureStreetInformation()
{
Expect.Once.On(builder).SetProperty("Address1").To("ADDR1");
}

[Test]
public void ShouldCaptureCspInformation()
{
Expect.Once.On(builder).SetProperty("Csp").To("CITY IL 60563");
}

This approach comes across as slightly odd because the expectations are set in the test but the test is run in the tear down. I actually think this is neater in some ways as it ensures you have one test class for each set of behaviours the only off putting thing is the naming convention of the attributes.

I won't bother continuing with the rest of Dave's article as it's just more of the same from here. The only thing I'd add is he does use one class per behaviour set (or context) so when he tests the behaviour of a string with ZIP code he uses a whole new test fixture. This can feel a little extreme in some cases as you get a bit of test class explosion but all in all it does make your life a lot easier.

I hope the translation helps all you .NET B/TDDers out there to free you from The Mockery.

Tip:
In more complex behaviours you may need to pass a value from one mock to another. In those instances you can do:

   Stub.On(x).Method(Is.Anything).Will(Return.Value(y));

TDD Anti-Patterns

It's a bit old now but I picked up a piece of code from a supplier that had the Generous Leftovers anti-pattern and it reminded me that every developer should have this list printed off and study it regularly.

Check out James Carr's TDD Anti-Patterns.

The Free Ride is probably the most common one and developers need to refer to "one assertion per test" to try and avoid this.

I think The Mockery is quite possibly the hardest anti-pattern to avoid mainly because we need a leap forward in the way Mock libaries work (what I call Quite Mocks). This will allow "one expectation per example". RSpec (used in the tutorial) has its own mock libary that supports Quite Mocks by passing a null_object argument. Unfortunately for us .NET developers out there such support doesn't exist. I have requested it on the NMock feature requests board but in the mean time you can create a helper class which uses reflection to stub out all the methods/properties you are not testing.

I am planning to 'translate' Dave Astels article to C# 'cos Ruby can be a bit tough on the eyes if you aren't used to it and as I mentioned already you need Quite Mocks (which don't exist) to really get it to work.

In the mean time I made my own contribution to the TDD Anti-Patterns with:

The Mad Hatter’s Tea Party
This is one of those test cases that seems to test a whole party of objects without testing any specific one. This is often found in poorly designed systems that cannot use mocks or stubs and as a result end up testing the state and behaviour of every peripheral object in order to ensure the object under test is working correctly.