Widgets Nick Hodges | A man's got to know his limitations

Cool New Tool: Delphi Code Coverage

By Nick at August 18, 2012 10:27
Filed Under: Delphi, Software Development, Unit Testing

Code Coverage is an interesting topic – Wikipedia defines it as “the degree to which the source code of a program has been tested.”  The idea is that you want to measure what percentage of the lines of code in your application are executed when you run your test suite.  The “perfect” test suite would execute every single line of code in your codebase.  Being able to definitively measure that goes a long way towards validating your testing suite and giving you confidence that your tests are thorough and testing everything that needs to be tested.

So I was really happy to run across the Delphi Code Coverage tool. I was intrigued and interested, so I downloaded it and gave it a look. And I really liked it.  I decided to run it through its paces by checking the code coverage of the unit tests for my THTMLWriter project. It didn’t take me long to figure out how to use it.   It’s written by Christer Fahlgren.  He blogged about it back in 2010.  It has a couple of other committers, and it’s been an active project throughout out 2012

The project includes this note: “The 1.0 release was made possible through the generous support of DevFactory.” I thought that was cool, and so I encourage you to go to their website and check out their services.

Some things to note off the bat:

So what did I do?  Well, first I pulled the source to make sure I had it.  Then, I went ahead and downloaded the RC7 build, which has one file in it:  codecoverage.exe.  I took that file and put it in a folder along my path so I can call it wherever I need it.

Then, I read the nice simple documentation.  I was just testing it out, so I ran everything manually via the IDE just to see how it all worked.  Eventually, you’d want to integrate this into your continuous integration. So here is a quick rundown of what I did and what I found. 

First, I opened up the project options for my THTMLWriter unit test application and told the Linker to create a MAP file for the project when I build it. The tools uses the MAP file to trace all the code paths that the application under test uses.

Next, I looked for the appropriate command  line switches. 

  • I used it –e switch to name the executable that would run. 
  • I used the –m switch to name the *.map file.
  • I used the –u switch to tell the tool what code unit I wanted analyzed.  Note that the switch wants the unit name, not the file name.  You can list as many units as you want after this switch.  Alternatively, you can use the –uf switch to point to a text file that has a list of unit names (one per line) to be examined.  In my case, I’m interested in the code coverage for the uHTMLWriter.pas unit.
  • I used the –html switch to indicate that I wanted the output to be an HTML file.  This would make it easier for me to look at the results in this “by hand” method of running things. 

The resulting command line was as follows:

codecoverage -e HTMLWriterTestAppTests.exe -m -u uHTMLWriter -html

Note that the above command line assumes that the current directory of your command prompt is the directory where the files in question are located.  I actually put the command line in a small batch file in the same directory.

So then I executed the command.  The tool popped up the GUI Runner for DUnit, I pressed the Run button, the tests ran, and when they were done, the tool finished up and produced some output in the form of an HTML file.  (It also provided a FastMM dialog at the end of its run, which took a few seconds to appear).


As noted, the result was two HTML files -- one summary file:


and a file that shows me the coverage for the uHTMLWriter unit.  That has a header in it that tells me that I have 98% code coverage.  Not bad!


But the real fun part is that the file contains a complete listing of the unit, color-coded to indicate which lines were executed (in green) and which weren’t (in purple). So 2% of my code isn’t covered?  So I scanned the file and came across this:


Looks like I never wrote a unit test for the OpenLabel method that takes a string parameter.  (I have one for the parameter-less OpenLabel).  Okay, so I went back, wrote a unit test for that one, and re-ran the code coverage tool, and now I have code coverage for that method:



Nice!  The tool also pointed out that I don’t test that a number of exceptions get properly raised, so I’ll get working on those, too.  I’d like to be able to run the report and have it return 100% for my coverage. 

Overall, this is a nice and powerful tool to help you make sure that your unit tests really are running every line of code in whatever you are unit testing.  It’s another great contribution to the Delphi community.  Thanks, Christer.

Flotsam and Jetsam #61

By Nick at August 11, 2012 06:54
Filed Under: Flotsam and Jetsam, Delphi, Tech Stuff
  • I’ve never been a hardware or network geek, but after I read this post by Jeff Atwood about how easy it was to set up custom firmware on a router a few notches above the “cheap one they basically give you when you sign up for cable internet”, I thought that I might try it some day.  I put the Atwood-recommended Asus RT-N16 on my Amazon wish list, and lo and behold, my parents kindly gave it to me for my birthday in July.  I actually left it sitting on the shelf for a few weeks, unsure if I really wanted to use it until a friend at work told me about Ooma.  Ooma is a phone service that works over your internet connection.  It’s not true VOIP, but similar.  Once you buy the device and get it set up, you basically get free phone service (I guess you pay some taxes or something each month, but only like $4 or something).  The Ooma should save me $50 a month.  Nice.  Anyway, if you have an Ooma, you really need a router that supports Quality of Service so that your phone calls don’t get aced out when your 13 year old starts downloading some huge game or something.  So today, I broke out the router, and used these instructions to flash the firmware on the Asus router, and now I’m up and running with TomatoUSB.  Very cool.   My next step is to buy the Ooma box and get that set up.  I’ll keep you all posted, as I know that you are eager to be updated on every single little thing I do.
  • You know, I just love all the stuff that the folks at DevJet are doing.  First, they are the impetus behind the Delphi Spring Framework, which as far as I am concerned you should treat like part of the Delphi RTL, as well as the really cool tool Documentation Insight.  Now they have release a new product that is the mirror to Documentation Insight – Documentation Generator.   You can pre-order it for 30% off, too.  What does it do?  Well, it takes all those great /// comments/documentation you wrote using Documentation Insight (which, by the way, is bundled with Delphi XE2) and turns it into online content.  For instance, here is the documentation for my HTMLWriter project.  And of course, all the documentation for the Spring4D project is online as well.  Nice.
  • There are some interesting Delphi book projects in the works:
  • Nick’s Opinion of the Week:  I think that if someone wants to open source their software, then they should do so.  And if they don’t want to open source their software, then they shouldn’t. And if you have a different opinion than the author of the software, then you should express it respectfully.  If your “advice” isn’t taken, then you should leave it be.  Just sayin’. 

How Not To Code #2: Don’t Use Boolean Method Parameters

By Nick at August 04, 2012 04:16
Filed Under: Delphi, How Not To Code

Okay, let’s start off with a question.  What do you think this little code snippet does?


Well, I’ll bet your first guess is that it processes customer input.  Good guess!  But what the heck does that False there mean?  It’s a parameter, and presumably it means something is, well, false, or that you don’t want the ProcessCustomerInput to do something, but how can you know?  You can’t.

Using Boolean parameters means that lose information for the reader of your code.  A Boolean parameter communicate nothing about the purpose or meaning of the parameter being passed.  Is False good or bad?  Safe or not safe?  Who knows?  Just as above, you can’t figure out at all what the parameter is supposed to mean or do if all you see is True or False

So if you see that in code, the first thing you’ll probably do is to go to the method declaration, and if the parameter is well named, you might figure out what the parameter does:

procedure ProcessCustomerInput(aKeepDuplicates: Boolean);

So there you go, now you know what the Boolean parameter does – apparently it tells you whether to keep the duplicates or not.  That’s great, but the original coder may not always be so kind and clear.  So if you must use a Boolean parameter, at least make the parameter name descriptive. 

Okay, I take it back – don’t actually ever use a Boolean parameter.  Instead, here’s what I suggest would make for much clearer code:

  TKeepDuplicates = (DoKeepTheDuplicates, DoNotKeepTheDuplicates);

procedure ProcessCustomerInput(aKeepDuplicates: TKeepDuplicates);

and that way you can call


And then your code is eminently readable and clear without having to look up the method declaration.

In addition, this way of doing things is expandable.  If your business rules change, and a third way of processing customer input appears, your code is ready.  With a Boolean parameter, you are stuck with the two options of True and False.

Easy to read, clear, and ready for the future.  Just like code should be.

Flotsam and Jetsam #60

By Nick at July 24, 2012 09:01
Filed Under: Flotsam and Jetsam, Delphi
  • Hey, Flotsam and Jetsam is back!  It’s been a while.  Sorry.
  • The folks at Helpinator are running a Absolutely Insane FireMonkey Demo contest.  I say you should give it a try.
  • Jason Southwell has an interesting project going over at KickStarterNakeyMonkey.  Cool idea.  I’ve heard about Kickstarter, but never really seen it in action. I love the idea – great way to spread the word about good ideas.  Not all good ideas need $15 million in venture capital.   Perhaps you want to get in on the ground floor of the project?
  • Okay, only like two real items, but we will take what we can get for the first Flotsam and Jetsam in quite a while, eh?

It's That Time Again: Gateway Ticketing Needs Delphi Developers

By Nick at July 02, 2012 07:05
Filed Under: Delphi, General, Software Development

My company, Gateway Ticketing, is hiring again. We are looking for Delphi developers. Actually, having Delphi skills is great, but we are mostly interested in smart people that know what they are doing when developing high-quality software.  We love Delphi and C#, but in the end, those are just languages and we know that it doesn’t ultimately matter what tool you know, but whether you really know how to write clean code.

Here are some reasons why you should consider working for Gateway:

  • We are a great place to work.  I love it here.  That this is a great place to work was so obvious to me that I moved my whole family clear across the country to join this team. 
  • We are serious about being serious about software development.  We aren’t messing around here.  While we have a large legacy code base, we are all about doing the right thing the right way with the right tools.  We insist on unit tests for your code.  We insist that you keep up with the latest innovations in writing code.  We insist that you view coding the same way that Rembrandt viewed painting.  
  • We love Delphi, and we live and  breathe it here.  We are doing cool things like using the Delphi Spring Framework, Dependency Injection, Unit Testing, and other fun stuff.
  • We use C# and ASP.NET for our eCommerce solution and all the cool stuff that goes along with that.
  • We are located in beautiful Boyertown, Pennsylvania.  This a great place to live and raise a family.  We are close to everything (including Philadelphia) but have that great small town feel.  I love living here, and you will too.
  • Our customers are some of the greatest and most fun places on earth.  We sell systems to the largest amusement parks, zoos, water parks, and museums all over the world.  This is a cool industry.  Who doesn’t love a good amusement park?

Okay, look – everyone says they want to hire “rock-star developers”.  Shoot, even we do it.  That’s all well and good, but the bottom line is that we are setting our standards really high.  And if doing that scares people off, well so be it.  We don’t want people who are scared off by high standards.  We want people who are looking for places with high standards.  We expect and demand your very best – anything less and you should find a job writing VB6 code. ;-) We really are creating a world-class place to build software, and we want folks like you to be a part of it.  You are up for that, right?

Relocation assistance is available.

And of course, here are the obligatory caveats.  We are definitely looking for people to live and work here in the Eastern Pennsylvania/Greater Philadelphia area.  Please note: we aren’t currently considering remote workers.  Naturally, you must be eligible to work in the United States. I'm sorry but right now we cannot sponsor H1B visas. :-(  We don’t care where you are from or who your parents were or what color your dog is or anything like that.  We are really only interested in what you can do.  And of course, we want you to know what we can do for you, too.

If that sounds like something good to you, please contact me.

TVirtualInterface: A Truly Dynamic and Even Useful Example

By Nick at June 30, 2012 08:25
Filed Under: Delphi, Software Development, Unit Testing


This is the third article in a series about using TVirtualInterface.  The two previous articles are TVirtualInterface: Interfaces without an Implementing Class and TVirtualInterface: Next Steps.

Okay, enough with the not-all-that-useful examples.  I mean, the previous articles were illustrative, but not really “real-world useful”.

The true usefulness of TVirtualInterface occurs when you use it to create code where you have no idea what interface the user of your code is going to try to implement.  All the examples so far have shown only implementing classes where you do know which interface is being used.  The exception so far is the TReportingVirtualInterface example which reports information on any interface you pass to it.  Since we have proven that you can use TVirtualInterface to do something useful, let’s take it a step further.

A practical use of TVirtualInterface is to create a mocking library for unit testing.  I’ve mentioned numerous times the Delphi Mocks Framework by Vince Parrett of FinalBuilder fame.  Another excellent implementation of a mocking framework (as well as a bunch of other very innovative and interesting stuff) is by Stefan Glienke as part of his Delphi Sorcery framework.  Both of these use TVirtualInterface to provide a mock implementation for any interface (though the Delphi Sorcery code implements its own version of TVirtualInterface that works with Delphi XE – very cool).  Both, of course, allow you to pass them any interface, and they’ll happily mock your interface for unit testing purposes.  So why not do an example here of a very simple mocking object that you can actually use if you want?


A while back I wrote an article called The Vocabulary of Unit Testing.  In it I described the distinction between a stub and a mock.  I defined a “stub” as “a fake that has no effect on the passing or failing of the test, and that exists purely to allow the test to run.”  So, how about we build a universal stub – a class that can pretend to be any interface you want, and not do anything at all.  That can’t be that tough, can it?

Well, we already have a class that can implement an interface, but we need to find a way for that class to actually be the interface.  If you want a stub, the stub has to actually be the interface type you are trying to stub out, right?

First, since we always code against abstractions, let’s declare an interface:

  ISimpleStub<T> = interface
    function InterfaceToCall: T;

And then let’s implement it with a descendent of TVirtualInterfaceEx<T>:

  TSimpleStub<T: IInvokable> = class(TVirtualInterfaceEx<T>, ISimpleStub<T>)
    procedure DoInvokeImpl(Method: TRttiMethod;  const Args: TArray<TValue>; out Result: TValue); override;
    function InterfaceToCall: T;

Because TSimpleStub<T> descends from TVirtualInterfaceEx<T>, it can implement any interface you pass to it.  It thus overrides DoInvokeImpl from  TVirtualInterfaceEx<T> as well as implementing InterfaceToCall from ISimpleStub<T>.

First, let’s look at DoInvokeImpl:

procedure TSimpleStub<T>.DoInvokeImpl(Method: TRttiMethod; const Args: TArray<TValue>; out Result: TValue);
  // Since this is a pure stub, don't do anything!

Not much to see here  – it doesn’t do anything.  And for a stub, that is fine.  That’s exactly what stubs are supposed to do – nothing.  We don’t care what happens when the methods get called, you just need to actually be able to call them.

That’s where the InterfaceToCall function comes in.  The class knows about the type of interface being stubbed because we are passing that type in as a parameterized type.  The class itself knows how to implement that interface.  There has to be a way to get an actual reference to that implemented interface, right?  This is where the InterfaceToCall method comes in:

function TSimpleStub<T>.InterfaceToCall: T;
  pInfo : PTypeInfo;
  pInfo := TypeInfo(T);
  if QueryInterface(GetTypeData(pInfo).Guid, Result) <> 0 then
    raise Exception.CreateFmt('Sorry, TSimpleStub<T> is unable to cast %s to its interface ', [string(pInfo.Name)]);

Since TSimpleStub<T> knows the type that T is, you can call QueryInterface on the type information about T itself to get a reference to the interface in question.  And of course, once you have that, you can pass that reference anywhere you need to stub out the interface – normally as part of unit testing.

So now, you can safely call methods on the stubbed interface.  For instance, given this interface:

IActuallyUseful = interface(IInvokable)
  procedure SayHello;
  function ReverseString(aString: string): string;
  function Multiply(x, y: integer): integer;

Writeln('Implementing a TSimpleStub');
SimpleStub := TSimpleStub<IActuallyUseful>.Create;
WriteLn('Nothing should appear between this and the next statement');
SimpleStub.InterfaceToCall.Multiply(4, 4);
WriteLn('Nothing should appear between this and the above statement');

Nothing happens when you call the interface methods, but that’s by design:  stubs should do nothing.  What you can do is call them as part of your unit testing:

  MyClassUnderTest := TSprocketThatTakesAnIWhatever.Create(SimpleStub.InterfaceToCall)


Okay, so there’s a useful, dynamic way to use TVirtualInterfaceTSimpleStub<T> will work great for a stub that you expect absolutely nothing from.  But sometimes you need a fake interface that does something more than just existing, and when that is the case, you are creating a mock.  In my unit testing definitions article, I defined a mock as “a fake that keeps track of the behavior of the Class Under Test and passes or fails the test based on that behavior.”  Thus, a mock needs to do more than exist like a stub –  it needs to behave in a way that you can define.   So how about we take TSimpleMock<T> and make it do a basic mocking function – responding in a specific way to a specific input.

One of the most common things that a mock interface does is to respond with “this” when passed “that”.  How about we create a simple mock class that lets you define a specific response to a method call?

First, of course, is an interface to code against:


  ISimpleMock<T> = interface(ISimpleStub<T>)
    procedure AddExpectation(aCallName: string; aReturnValue: TValue);

The interface augments (“inherits from” is not quite right with interfaces) ISimpleStub<T> and adds the AddExpectation method.  This is the method that we’ll use to tell the mock out to respond when and interface method gets called. 

Here’s the implementing class:

  TSimpleMock<T: IInvokable> = class(TSimpleStub<T>, ISimpleMock<T>)
    FActions: TDictionary<string, TValue>;
    procedure DoInvokeImpl(Method: TRttiMethod;  const Args: TArray<TValue>; out Result: TValue); override;
    constructor Create;
    destructor Destroy; override;
    procedure AddExpectation(aCallName: string; aReturnValue: TValue);

The first thing to notice is that TSimpleMock<T> inherits  from TSimpleStub<T>, thus enabling it to “be” any interface it wants as our stub was. And of course it also implements the  AddExpection method.  It takes as parameters the name of the method on the interface that you can call, as well as a return value for when that method gets called.  In this way you can define the behavior of the mock class however you want.

This very simple mocking example assumes that you are going to be mocking only function calls as methods on an interface. Within the confines of our simple example, it doesn’t make sense to mock procedures – they basically don’t do anything as far as the simple example is concerned.  Real mock frameworks are able to keep track of whether a procedure is called, how many times it does get called, and other things associated with procedures.  This simple example also doesn’t care what parameters you pass in, it will merely return a value whenever the named method is called.   Remember, this is a simple – but useful in specific situations -- example.  Winking smile 

The implementation of TSimpleMock<T> is pretty, well, simple.  Internally, it uses a TDictionary<TKey, TValue> to keep track of the method calls and the resulting responses that are added via the AddExpectation call.  Here is the implementation of AddExpectation :

procedure TSimpleMock<T>.AddExpectation(const aCallName: string; aReturnValue: TValue);
  FActions.Add(aCallName, aReturnValue);

When you add an expectation, the class keeps track of it.  When you then call that method on the interface, it is able to retrieve the expected return value from the dictionary and return it:

procedure TSimpleMock<T>.DoInvokeImpl(Method: TRttiMethod; const Args: TArray<TValue>; out Result: TValue);
  Result := FActions[Method.Name];

(The obvious shortcoming here is no error handling – you’ll get an exception if you try to call a method on the interface that doesn’t  have an expectation entry.  Another shortcoming is that the parameters passed mean nothing – a real mocking framework would be able to provide specific responses for specific parameter inputs.    I’ll leave correcting this problem as an exercise to the reader.  Smile )

So now, when we exercise this class, it will actually return stuff that you tell it to:

This code:

WriteLn('IActuallyUseful with ISimpleMock');
SimpleMock := TSimpleMock<IActuallyUseful>.Create;
SimpleMock.AddExpectation('Multiply', 99);
SimpleMock.AddExpectation('ReverseString', 'This is actually working');
WriteLn(SimpleMock.InterfaceToCall.Multiply(6, 7));
WriteLn(SimpleMock.InterfaceToCall.ReverseString('This does not matter'));

has the following output:


Note that the responses are not what you think they would be based on the parameters (you think that 6 times 7 would return 42…), but what you told them to be in the AddExpectation call.

Now, you can use ISimpleMock<T> to provide specific feedback for a given method call.  Maybe you have an interface method which returns a Boolean value that you want to test. You can use ISimpleMock<IBooleanMethod> to test what happens when the method returns True as well as when that method returns False


Okay, so there you have it:  A useful implementation of TVirtualInterface.  Though the above examples are really simple, they can actually be used in real world testing – particularly the ISimpleStub<T> implementation. Stubbing is common in unit testing, and even though it is a very basic implementation, it can be used to stub out any interface.

None of this is useful if you know what interface you need and how you are going to implement it.  But there are cases when you don’t know what interface you will need for a particular problem, and you need to be able to flex to whatever interface the situation calls for.  Mocking and stubbing are perfect examples.  That’s a powerful and useful thing to be able to do.  Hopefully this little series has helped you see that.

TVirtualInterface: Next Steps

By Nick at June 13, 2012 21:48
Filed Under: Delphi, Software Development

Okay, so my last article was pretty fun – you got a look at TVirtualInterface and how you can use it to implement any interface.  Now, I want to be clear – the code in that article was demo code.  That is, it was purely for illustrative purposes.  I can’t think of any reason why you’d actually, in the real world, implement an interface that way. But after reading it, you should be able to see how TVirtualInterface works and how you can get it to do what you want. 

Now, in that article I promised you that my next blog post on the topic would be an example of using TVirtualInterface in a more useful manner.  But I guess I lied, because this blog post is about how you can create a slightly better version of TVirtualInterface.

So a while back, I wrote a post about getting you to “think generically” and how generics (or as I prefer to think of them, parameterized types) are useful in more ways than just collections and lists.   Well, I got to looking at TVirtualInterface and I thought, “You know, here’s a class that actually requires type information about a given type, and in order for it to do anything useful, you have to give it a type in the constructor, so hmmm…….”.  And you can guess where I went from there. 

So, consider the following class declaration:


  TVirtualInterfaceEx<T: IInvokable> = class(TVirtualInterface)
    procedure DoInvoke(Method: TRttiMethod;  const Args: TArray<TValue>; out Result: TValue);
    procedure DoInvokeImpl(Method: TRttiMethod;  const Args: TArray<TValue>; out Result: TValue); virtual; abstract;
    constructor Create;

This is a pretty simple descendent for TVirtualInterface.  The most obvious thing is that it takes a parameterized type T which is constrained to be an interface descending from IInvokable.  That enables you to explicitly declare what interface TVirtualInterfaceEx is going to implement.  You should notice, too that TVirtualInterfaceEx is an abstract class, as the DoInvokeImpl method is abstract.

So, once you have the parameterized type, you know everything you need to implement the interface.  As you know from the previous article, the thing you need to do is to provide an implementation of DoInvoke.  So TVirtualInterfaceEx employs the technique I’ve described before whereby you implement the interface in the base class and provide a “real” implementation in a separate method invoked by the base class.  So, the implementation looks like this:

constructor TVirtualInterfaceEx<T>.Create;
  inherited Create(TypeInfo(T), DoInvoke);

procedure TVirtualInterfaceEx<T>.DoInvoke(Method: TRttiMethod;  const Args: TArray<TValue>; out Result: TValue);
  DoInvokeImpl(Method, Args, Result);

The constructor is pretty simple – it is parameter-less and  calls a sibling constructor, passing in the TypeIinfo for your interface and the DoInvoke method which is of type TVirtualInterfaceInvokeEvent.  The code for DoInvoke method simply calls the DoInvokeImpl method, which, because it is abstract, descendent classes must override.

Thus, to use this class, all you need to do is to descend from it and provide an interface as a parameterized type and an implementation for DoInvokeImpl.   So, if we wanted to implement the IActuallyUseful interface from the previous example, all we need to do is:

  TActuallyUsefulEx = class(TVirtualInterfaceEx<IActuallyUseful>)
    procedure DoInvokeImpl(Method: TRttiMethod;  const Args: TArray<TValue>; out Result: TValue); override;

implementing DoInvokeImpl with the same code that was in the DoInvoke event of the TActuallyUseful class. 

By the way, I should mention that the code for these demos on TVirtualInterface, including a sneak peek at the code for the next article, is available as part of my demo code project on BitBucket.

This isn’t anything really fancy, but I liked it because it simplified the process of creating virtual interface implementations and provided another example of a good use for parameterized types.  I also like what I mentioned previously, that it clearly declares what interface it is implementing.

Anyway, I thought it was a cool little wrapper/descendent for the TVirtualInterface class.  And I promise that the next blog post on this stuff will show an example of using it in a truly dynamic way.

TVirtualInterface: Interfaces without an Implementing Class

By Nick at June 10, 2012 05:37
Filed Under: Delphi, Software Development

I would be really disappointed if we spent an hour discussing software development and I didn’t at least once say to you "Program against interfaces, not against implementations".  It’s sort of a mantra for me – a way of life if you will.  It’s a bedrock principle of development as far as I’m concerned. Programing against interfaces and not against implementations is the only way to truly decouple your code.  And if you don’t believe that decoupling your code is important, I’d like you to stop reading right now, get a small ball-peen hammer, and keep hitting yourself in the forehead until you change your mind.

So if you’ve made it this far, you’ll know that implementing interfaces is needed to use them.  You have to put some code behind an interface to make it do anything.  Normally, this is done with an implementing class:

  ISprocketProcessor = interface
    procedure ProcessSprockets;

  TSprocketProcessor = class(TInterfacedObject, ISprocketProcessor)
    procedure ProcessSprockets;

But what if you could implement an interface without having a specific class?  What if there were a way to implement any interface with a single module of code? What if you could decide at runtime how to implement an interface?  Would I even be asking these questions and writing this if those things weren’t possible?

So, yes, obviously it is.  Delphi XE2 introduces a very cool new class called TVirtualInterface. Its purpose is to allow you to descend from it and respond to any interface dynamically.  If you think about that for a second you’ll realize that this is pretty powerful. For instance, it’s the thing that lets the awesome Delphi Mocks Framework provide a mock implementation of any interface that you pass to it.

Generally, when you implement an interface, you provide a class that implements it in a specific way – i.e. that implementation becomes static at runtime. There are ways – typically via Dependency Injection – that allow you to choose an implementation, but even then you are limited to a specific set of implementations.   TVirtualInterface allows you to dynamically -- i.e. at runtime – determine how an interface will be implemented.  The examples in this article will show a fixed way to implement TVirtualInterface so you can get the basics of how to use TVirtualInterface.  In a future article, we’ll look at more dynamic ways to use this sweet class.

Here’s the public interface for TVirtualInterface:

  { TVirtualInterface: Creates an implementation of an interface at runtime.
    All methods in the Interface are marshaled through a generic stub function
    that raises the OnInvoke event.}
  TVirtualInterface = class(TInterfacedObject, IInterface)
    function QueryInterface(const IID: TGUID; out Obj): HResult; virtual; stdcall;
    { Create an instance of TVirtualInterface that implements the methods of
      an interface.  PIID is the PTypeInfo for the Interface that is to be
      implemented. The Interface must have TypeInfo ($M+). Either inherit from
      IInvokable, or enable TypeInfo for the interface. Because this is an
      TInterfacedObject, it is reference counted and it should not be Freed directly.
    constructor Create(PIID: PTypeInfo); overload;
    constructor Create(PIID: PTypeInfo; InvokeEvent: TVirtualInterfaceInvokeEvent); overload;
    destructor Destroy; override;
    { OnInvoke: Event raised when a method of the implemented interface is called.
      Assign a OnInvoke handler to perform some action on invoked methods.}
    property OnInvoke: TVirtualInterfaceInvokeEvent read FOnInvoke write FOnInvoke;

First, you should notice that TVirtualInterface descends from TInterfacedObject and implements IInterface.  The three methods of IInterface are implemented to allow the class to be properly reference counted like any other interface-implementing class.  Second, the interface that you want to implement with it needs to have TypeInfo enabled for it.  The easiest way to make that happen is to descend your interface from IInvokable.  Otherwise, you’ll need to use the {$M+} switch for your interface. Notice, too, that the comment above the class declaration says what I said early – using TVirtualInterface will let you, well, do anything you want with an interface at runtime.  Cool. 

So, in order to actually make TVirtualInterface do something, you need to create a descendent class and provide two things:  a constructor and an implementation of the DoEvent method.

Here’s an TVirtualInterface descendent that is as simple an example as I could think of:

  TSimplestVirtualInterface = class(TVirtualInterface)
    constructor Create(PIID: PTypeInfo);
    procedure DoInvoke(Method: TRttiMethod;  const Args: TArray<TValue>; out Result: TValue);

constructor TSimplestVirtualInterface.Create(PIID: PTypeInfo);
  inherited Create(PIID, DoInvoke);

procedure TSimplestVirtualInterface.DoInvoke(Method: TRttiMethod;
  const Args: TArray<TValue>; out Result: TValue);
  WriteLn('You called a method on an interface');

The only thing this will do is to write out to the console – no matter what.  You can pretend it implements any interface, and no matter what you call on that interface, it will merely write to the console. 

The constructor takes a single parameter, PIID, which is is the TypeInfo for the interface you want to “implement”.  (That’s why the interface in question must have the {M+} switch – usually via IInvokable.)  Inside the constructor, a call to a different constructor is made.  The PIID parameter is passed in, as is a reference to DoInvoke, which is a method that matches the type TVirtualInterfaceInvokeEvent.  Thus, the constructor is basically saying “Here is the type of information for the interface I’m implementing, and the method you should run whenever a method is called on that interface.”

In our case, the DoInvoke method only does one thing no matter what – writes to the console.

So, for instance, say you declare an interface:

  IGoStop = interface(IInvokable)
    procedure Go;
    procedure Stop(aInteger: integer);

And then you run the following code in a console application:

   GoStop := TSimplestVirtualInterface.Create(TypeInfo(IGoStop)) as IGoStop;

the console output will look like this:



You see the output twice because the code called two methods.  It doesn’t matter what you call – that output will happen no matter what.  It doesn’t matter what interface you pass in or what method you call, the result will be the same.

But of course that isn’t useful – to be of any use, you need to be able to know what is getting called, what is getting passed in, and respond accordingly.

Well, you can do that, because if you look at the signature of the DoInvoke method, you’ll note that when it gets called by the TVirtualInterface.OnInvoke event, it gets passed the RTTI for the method that was called, an array of TValue that contain the interface itself and all the arguments that the method was passed, as well as an out parameter of type TValue that allows you to return a value if the method being called is a function. 

So how about we simply use the DoInvoke event to report out what all that information that it receives.

procedure TReportingVirtualInterface.DoInvoke(Method: TRttiMethod;
  const Args: TArray<TValue>; out Result: TValue);
  Arg: TValue;
  ArgType, ArgName: string;
  TempKind: TTypeKind;
  Write('You called the ', Method.Name, ' method ');
  if Length(Args) > 1 then
    Writeln('and it has ', Length(Args) - 1,' parameters:');
    for Arg in Args do
      TempKind := Arg.Kind;
      if TempKind <> tkInterface then
        ArgName := Arg.ToString;
        ArgType := Arg.TypeInfo.Name;
        Writeln(ArgName, ' which is of the type ', ArgType);
  end else
    Writeln(' and it has no parameters.');

This code simply looks over and reports out about the Method and Args parameters that get passed in when the interface is invoked.  The very first item in the array is always type information about the interface itself, and the rest are the parameters, in order, as they were passed in.  Here, the code simply reports out their values and types, but of course, you can process them as you please. 

Again, that is interesting information, but it’s just a step towards understanding how TVirtualInferface works.  Let’s create something that actually does what we want it to.

Here’s a basic interface:

  IActuallyUseful = interface
    procedure SayHello;
    function ReverseString(aString: string): string;
    function Multiply(x, y: integer): integer;

Then, below is the DoInvoke method for a TActuallyUseful class that will actually do what the interface purports to do:

procedure TActuallyUseful.DoInvoke(Method: TRttiMethod;
  const Args: TArray<TValue>; out Result: TValue);
  if UpperCase(Method.Name) = 'SAYHELLO' then
    WriteLn('Hello World!');
  end else
    if UpperCase(Method.Name) = 'REVERSESTRING' then
      Result := ReverseString(Args[1].AsString)
    end else
      if UpperCase(Method.Name) = 'MULTIPLY' then
          Result := Args[1].AsInteger * Args[2].AsInteger;
      end else
        raise Exception.Create('Bad Parameter name was passed in to the DoInvoke method');

This code should be fairly self-explanatory.  It simply checks for the name of the method that was called, and then executes code using the parameter information passed in the Args parameter.  If the call is a function, the Result parameter is used to return a value.   

You should  remember that the initial item in the Args array (that is, the one at the “zero-eth” position) is the interface type itself.  The code also makes assumptions about the number and types of the parameters.  Since the code can only be invoked by the methods declared on IActuallyUseful interface, the code can make safe assumptions about the types and order of the parameters.

Now all of this code above is fairly straight-forward – we are basically simulating an implementing class in our examples.  Nothing is truly dynamic.  The code here merely shows simple examples of how TVirtualInterface works in a fairly static way. You should now be able to see how you could dynamically implement an interface using a TVirtualInterface descendent.

Coding against interfaces is critical for writing good, clean code.  TVirtualInterface is just another powerful tool in your toolbox for doing just that.

Fun Code of the Week #4

By Nick at June 08, 2012 06:14
Filed Under: Delphi, Fun Code

Adapted from my answer on StackOverflow:

function RemoveChars(const aString: string; aCharsToRemove: TSysCharSet): string;
  C: Char;
  Result := '';
  for C in aString do
    if not CharInSet(C, aCharsToRemove) then
      Result := Result + C;

The Vocabulary of Unit Testing

By Nick at May 03, 2012 14:20
Filed Under: Delphi, Software Development, Unit Testing

I talk a lot about unit testing.  And why shouldn’t I?  Unit testing is the key to writing clean, maintainable code.  If you concentrate on writing code that is easily testable, you can’t help but end up with decoupled, clean, high-quality code that is easy to maintain.  What’s not to like?

But sometimes, there are questions over the definition of terms when it comes to unit testing.  For instance, what, exactly, is a “unit”?  What does “mocking” mean?  How do I know whether I actually am doing unit testing?  In this article, I try to clear up some of those definitions.

What is a “Unit”?

The first question that comes up when discussing unit testing is, well, what is a unit?  You can’t do unit testing without knowing what a unit is.

When it comes to unit testing, I view a “unit” as any discreet  module of code that can be tested in isolation.  It can be something as simple as a stand-alone routine (think StringReplace or IncMonth), but normally it will be a single class and its methods.  A class is the basic, discrete code entity of modern languages. In Delphi, classes (and records which are conceptually very similar) are the base building blocks of your code.  They are the data structures that, when used together, form a system. 

In the world of unit testing, that class is generally referred to as the “Class Under Test (CUT)” or the “System Under Test”.  You’ll see those terms used extensively – to the point where it is strongly recommended that you use CUT as the variable name for your classes being tested.

Definition:  A unit is any code entity that can be tested in isolation, usually a class. 

Am I Actually Doing Unit Testing?

So when you are doing unit testing, you are generally testing classes. (And for the sake of the discussion, that will be the assumption hereafter…)  But the key thing to note is that when unit testing a class, you are unit testing the given class and only the given class.   Unit testing is always done in isolation – that is, the class under test needs to be completely isolated from any other classes or any other systems.  If you are testing a class and you need some external entity, then you are no longer unit testing.  A class is only “testable” when it’s dependencies can be and are “faked'”, and thus tested without any of its real external dependencies.  So if you are running what you think is a unit test, and that test needs to access a database, a file system, or any other external system, then you have stopped doing unit testing and you’ve started doing integration testing. 

One thing I want to be clear about:  There’s no shame in doing integration testing.  Integration testing is really important and should be done.  Unit testing frameworks are often a very good way to do integration testing.  I don’t want to leave folks with the impression that because integration is not unit testing, you shouldn’t be doing it – quite the contrary.   Nevertheless, it is an important distinction.  The point here is to recognize what unit tests are and to strive to write them when it is intended to write them. By all means, write integration tests, but don’t write then in lieu of unit testing. 

Think of it this way:  Every unit test framework – DUnit included – creates a test executable.  If you can’t take that test executable and run it successfully on your mother’s computer in a directory that is read only, then you aren’t unit testing anymore. 

Definition: Unit testing is the act of testing a single class in isolation, completely apart from any of it’s actual dependencies.

Definition: Integration testing is the act of testing a single class along with one or more of its actual external dependencies.

What is an Isolation Framework?

Commonly, developers have used the term “mocking framework” to describe code that provides faking services to allow classes to be tested in isolation.  However, as we’ll see below, a “mock” is actually a specific kind of fake class, along with stubs.  Thus, it is probably more accurate to use the term “Isolation Framework” instead of “Mocking Framework”.  A good isolation framework will allow for the easy creation of both types of fakes – mocks and stubs. 

Fakes allow you to test a class in isolation by providing implementations of dependencies without requiring the real dependencies. 

Definition: An isolation framework is a collection of code that enables the easy creation of fakes. 

Definition: A Fake Class is any class that provides functionality sufficient to pretend that it is a dependency needed by a class under test.  There are two kind of fakes – stubs and mocks.

If you really want to learn about this stuff in depth, I strongly recommend you read The Art of Unit Testing: With Examples in .Net by Roy Osherove.  For you Delphi guys, don’t be scared off by the C# examples -- this book is a great treatise on unit testing, and gives plenty of descriptions, proper techniques, and definitions of unit testing in far more detail than I’ve done here.  Or, you can listen to Roy talk to Scott Hanselman on the Hanselminutes podcast.  I openly confess that this blog post is a faint echo of the great stuff that is included in both the book and the podcast.  If you really want to get your geek on, get a hold of a copy of xUnit Test Patterns: Refactoring Test Code by Gerard Meszaros.  This heavy tome is a tour de force of unit testing, outlining a complete taxonomy of tests and testing patters.  It’s not for the faint of heart, but if you read that book, you’ll know everything there is to know and then some. 


A stub is a class that does the absolute minimum to appear to be an actual dependency for the Class Under Test.  It provides no functionality required by the test, except to appear to implement a given interface or descend from a given base class.  When the CUT calls it, a stub usually does nothing.  Stubs are completely peripheral to testing the CUT, and exist purely to enable the CUT to run.  A typical example is a stub that provides logging services.  The CUT may need an implementation of, say, ILogger in order to execute, but none of the tests care about the logging.  In fact, you specifically don’t want the CUT logging anything.  Thus, the stub pretends to be the logging service by implementing the interface, but that implementation actually does nothing.  It’s implementing methods might literally be empty.  Furthermore, while a stub might return data for the purpose of keeping the CUT happy and running, it can never take any action that will fail a test.  If it does, then it ceases to be a stub, and it becomes a “mock”.

Definition: A stub is a fake that has no effect on the passing or failing of the test, and that exists purely to allow the test to run.


Mocks are a bit more complicated.  Mocks do what stubs do in that they provide a fake implementation of a dependency needed by the CUT.  However, they go beyond being a mere stub by recording the interaction between itself and the CUT.  A mock keeps a record of all the interactions with the CUT and reports back, passing the test if the CUT behaved correctly, and failing the test if it did not.  Thus, it is actually the Mock, and not the CUT itself, the determines if a test passes or fails.

Here is an example – say you have a class TWidgetProcessor.  It has two dependencies, an ILogger and an IVerifier.  In order to test TWidgetProcessor, you need to fake both of those dependencies.  However, in order to really test TWidgetProcessor, you’ll want to do two tests – one where you stub ILogger and test the interaction with IVerifier, and another where you stub IVerifier and test the interaction with ILogger.  Both require fakes, but in each case, you’ll provide a stub class for one and a mock class for the other. 

Let’s look a bit closer at the first scenario – where we stub out ILogger and use a mock for IVerifier.  The stub we’ve discussed – you either write an empty implementation of ILogger, or you use an isolation framework to implement the interface to do nothing.  However, the fake for IVerifier becomes a bit more interesting – it needs a mock class.  Say the process of verifying a widget takes two steps – first the processor needs to see if the widget is in the system, and then, if it is, the processor needs to check if the widget is properly configured.  Thus, if you are testing the TWidgetProcessor, you need to run a test that checks whether TWidgetProcessor makes the second call if it gets True back from the first call.  This test will require the mock class to do two things:  first, it needs to return True from the first call, and then it needs to keep track of whether or not the resulting configuration call actually gets made.  Then, it becomes the job of the mock class to provide the pass/fail information – if the second call is made after the first call returns True, then the test passes; if not, the test fails.  This is what makes this fake class a mock:  The mock itself contains the information that needs to be checked for the pass/fail criteria.

Definition: A mock is a fake that keeps track of the behavior of the Class Under Test and passes or fails the test based on that behavior.

Most isolation frameworks include the ability to do extensive and sophisticated tracking of exactly what happens inside a mock class. For instance, mocks can not only tell if a given method was called, it can track the number of times given methods are called, and the parameters that are passed to those calls.  They can determine and decide if something is called that isn’t supposed to be, or if something isn’t called that is supposed to be.  As part of the test setup, you can tell the mock exactly what to expect, and to fail if that exact sequence of events and parameters are not executed as expected.  Stubs are fairly easy and straightforward, but mocks can get rather sophisticated.

I’ve written about the Delphi Mocks framework in a previous post.  It takes advantage of some cool new RTL features in Delphi XE2.  It’s also a very generous and awesome gift to the Delphi community from Vince Parrett, who makes the very awesome FinalBuilder. If you have XE2 and are doing unit testing, you should get Delphi Mocks and use it.  If you don’t have XE2 and are doing unit testing, you should upgrade so you can start using this very valuable isolation framework.

But again, the whole point here is to test your classes in isolation; you want your CUT to be able to perform its duties without any outside, real, external dependencies.

Thus, a final definition:  Unit testing is the testing of a single code entity when isolated completely from its dependencies. 

Fun Code of the Week #3

By Nick at May 01, 2012 08:44
Filed Under: Fun Code, Delphi
procedure ShowHourGlass(Proc: TProc);
  Screen.Cursor := crHourGlass;
    Screen.Cursor := crDefault;

Tweet Expansion: Butt Time and Brain Time

By Nick at April 29, 2012 08:53
Filed Under: Delphi, Leadership, Software Development, Tweet Expansion

A while back I tweeted the following:

In software development, we often measure Butt Time, when what we need from developers is Brain Time -- which is much harder to measure.

Some tweets call for further explanation and expansion, and so I’ve added a new category called Tweet Expansion to cover posts that do just that.

Here at Gateway Ticketing, we have an interesting development and business model.  At our core, we are an ISV.  We sell a software package that we build to customers.  But, we also will customize our software to meet customer specifications.  That makes us sort of a VAR to our own product.  Thus, we do both enhancements based on customer requests and our own internal product development projects to make our product more valuable in the marketplace. 

This distinction – between internal projects and projects driven by specific customer requirements – makes for some challenging project management.  But we have a solid team here at Gateway, and we make it all work.  But because we do work that amounts to us being consultants, we end up having to closely track our developer time.  We do that for a number of business reasons, the main one, of course, is profitability.  You need to track your time to ensure that you are actually making money on a given endeavor.

Now I know that no one really likes to track their time.  It’s a pain.  It’s challenging to be accurate.  It’s hard to get time properly categorized.  But it is also invaluable for making those important business decisions. 

But there is a bigger problem with measuring time.  The only thing you can really measure is “Butt Time”.  Butt Time is the actual amount of time someone has their butt in a chair while working on an issue.  You need Butt Time to get any work done, of course.

But Butt Time isn’t really what you want from your developers.  Butt Time isn’t at all equivalent to productive development time.  Butt Time includes reading email, answering questions and generally handling any number of interruptions, meetings, and other distractions.  And those distractions, however minor, break a developer’s concentration.

And when you get right down to it, development is all about concentration.  With a coding project of any size at all, doing development requires your complete focus and concentration.  You need to build up complex data structures and patterns in your mind in order to really be productive.  Doing so takes time --  I’ve heard it described as building a house of cards in your mind.  Building that house of cards can take upwards of fifteen minutes depending upon the project.  But here’s the bummer:  It only takes a second for that house of cards to come tumbling down.  One distraction can make your fifteen minute investment disappear. 

And of course, time spent in “The Zone” – with that house of cards constructed and true, highly productive work getting done – is what we all are seeking.  We’ve all probably had that awesome experience of getting into that zone for hours at a time and wondering where the time went.  We know how cool that is – and how precious.  That’s what we want to measure – Brain Time.

But that’s a really hard thing to do.  Getting accurate, meaningful Butt Time measurements is difficult enough.  But how in the world can you actually measure Brain Time?

I’ll argue that you really can’t.  In the end, Butt Time is only a poor proxy for Brain Time.  What we need to do is to try to increase the Butt Time to Brain Time ratio by providing an environment where Brain Time is maximized as a percentage of total Butt Time.

There are ways to do that – ensuring that your developers have an office with a door that they can close is an important first step.  The book Peopleware is really the Bible for this, and Joel Spolsky has talked a lot about it as well.  Uninterrupted quite time is the key.  Leaving developers alone is the key to maximizing Brain Time.

Seriously – you need to get and read Peopleware if you have anything at all to do with leading developers.  This is the definitive book on managing software developers.  Be sure to get the Second Edition.  The physical book is, I believe, out of print, causing the price to be pretty high,  but I was delighted to notice that you can now order it on the Kindle

Another thing we need to do is to respect – indeed, celebrate – those developers that are quiet and don’t say much.  We have a not small number of developers here at Gateway that, well, don’t say much at all.  They come to work, write great code, and go home.  They don’t have a lot to say.  But sadly, we don’t always respect this.  I’m as guilty of anyone of too often saying super-clever things like “Stop being so boisterous, Meredith” or “Did you say six words today?”, instead of recognizing that Meredith is maximizing her Brain Time and, by being quiet, not breaking other team members’ concentration.  Being quiet is a very valuable virtue in a software developer – both because they themselves are being productive and they aren’t breaking other’s concentration -- and we should give honor and respect to that.

Butt Time is easy to come by and fairly easy to measure.  Brain Time, however, is a precious and hard to measure commodity that needs to be nurtured and respected.

Flotsam and Jetsam #59

By Nick at April 23, 2012 05:39
Filed Under: Flotsam and Jetsam
  • The comments are working again.  My apologies go out to those folks who were kind enough to try to comment but weren’t able to.  I don’t know what the problem was – it went away when I deleted my “Little boxes” box in the sidebar.  When I rebuilt it using pretty much the same code, it all kept on working.  Gremlins, I guess.  In any event, all should be well, and thank you to those of you who took the time to let me know about the problem.
  • More on Delphi Marketing:  I wrote about Delphi marketing a little while back, and here’s more proof that they are busy and really doing a great job.  Tim Del Chiaro has the list of online webinar and events that happened just in the first quarter of this year alone. That is a very long and interesting list of webinars you can view to learn about Embarcadero products, what they can do, and why you might want to buy them.  That’s what marketing folks do – let you know that the product exists, what it does and why you need it.  More good stuff continues to come out of the folks in Scotts Valley, and you should be giving credit where credit is due if you aren’t.
  • I’m a big fan of Documentation Insight by DevJet, and they have recently released version 2.0 of this great IDE tool. I heartily recommend that you buy it and start writing /// comments for your library code – and any code at all, for that matter.  Visit the What’s New page for information about this excellent tool. 
  • Jeff Duntemann pointed to these really cool pictures of the interior of the Hindenburg.  Now, of course, the name “Hindenburg” is synonymous with “horrible, flaming disaster”, but one would assume that had the thing not been filled with hopelessly flammable hydrogen, that blimp travel might have become popular.  I don’t know about you, but I think that a trip on such a ship would be really, really cool.  Blimps are a common site today – no big sporting event happens without the famous overhead shots from the Goodyear Blimp – and I for one would love to take a trip across the United States in a blimp at a reasonable altitude for seeing the sites.  I’m surprised such a service isn’t available – I can’t imagine that I’d be alone in such a desire.
  • Dennis Landi – long time Delphi guy – is looking for a Delphi developer in the Washington, DC area.  

Comments Working.

By Nick at April 21, 2012 23:27
Filed Under: General

Okay, it looks like comments are working now.  

It seems that my little box of flair (links to Facebook, etc) was causing the problem.  I deleted it for now.

What a bother.

Comments Broken?

By Nick at April 11, 2012 10:05
Filed Under: General

I notice that I haven't had any comments since April 1, and now I've gotten some emails from some of you kind folks pointing out that commenting doesn't work.  

Is that still the case? (Feel free to answer at if it is....)

Sorry about that -- I'm not sure what the issue is.

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The views I express here are entirely my own and not necessarily those of any other rational person or organization.  However, I strongly recommend that you agree with pretty much everything I say because, well, I'm right.  Most of the time. Except when I'm not, in which case, you shouldn't agree with me.