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Test Driven Development in Delphi: The Basics

, 14 Dec 2012 CPOL
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A few examples.

I intend to write a Test Driven Development (TDD) series, targeted for Delphi developers. I will use DUnit, the unit testing framework for Delphi.

Note folks that the purpose of this is not to discuss the pros and cons of TDD, Unit Testing or whatsoever. The purpose is just to give a few examples. I would love if you help me when the complexity starts climbing.

If needed, for a quick understanding of what TDD or Unit Testing is, refer to the links above, or check out the book at the end of the article.

In TDD you don’t write the application code first, instead you write the test cases first. The TDD cycle is as follows:

  1. At the beginning you just write one test, and later on, more tests can be added.
  2. Make sure the initial test fails; this will validate the test harness.
  3. Write some code to pass the test. Important: don’t over-code. Just add the code needed to pass the test and period. The code does not have to be elegant at this point.
  4. Run the test: if it fails, then you have to go back to step 3 and fix your code in order to pass the test. When you succeed, then move on to step 5.
  5. Improve and optimize your code: make it elegant, more efficient, avoid duplications, etc, etc. This is called code refactoring.
  6. When refactoring your code, maybe, by accident, you break the functionality. How can you be sure that everything is working as it should? Just re-run your test and it will tell you if the previous refactoring introduced a failure or not.
  7. Go to step 1 and add a new test if needed.

The example: let’s consider the chess game. The goal will be to implement the code to verify whether a piece is placed in a valid position within the board. We are only going to implement one test: SetPositionTest.

I will number the columns (X coordinate) from 1 to 8 starting at the bottom left-hand corner. In the same way, I will number the rows (Y coordinate) from 1 to 8 starting at the bottom left-hand corner.

8
7
6
5
4
3
2
1 2 3 4 5 6 7 8

For a step by step tutorial of how to use, configure and setup DUnit you can read the English or Chinese versions of the tutorial.

Initially, the testing code should look like this:

unit ChessPiecesTests;

interface

uses
   TestFrameWork;

type
  TPieceTest = class(TTestCase)
  published
    procedure SetPositionTest;
  end;

implementation

uses
  ChessPieces;

{ TPieceTest }

procedure TPieceTest.SetPositionTest;
begin
end;

initialization
  TestFramework.RegisterTest(TPieceTest.Suite);
end.

If you run that test, it will succeed since no checks are being performed within the SetPositionTest procedure.

Each test is composed by one or more checks. I suggest adding the checks little by little. Every time you add a check, you should add business code to pass the corresponding test.

Now, let’s make the test fail on purpose. For that, let’s add one check to the SetPositionTest procedure.

procedure TPieceTest.SetPositionTest;
begin
  Check(True = False, '');
end;

True is never False. So, this test will fail. If it doesn’t fail, then something is wrong with you test harness. Fix it. You can remove this initial check once you run the test and it fails.

Now, let’s add a real check to our test. Something like this:

procedure TPieceTest.SetPositionTest;
var
  Piece: TPiece;
begin
  Piece:= TPiece.Create;
  try
    //Test trivial (normal) workflow
    Check(Piece.SetPosition(4, 4) = True, '');
  finally
    Piece.Free;
  end;
end;

If you run this test, you will get a compilation error! Yes, that’s right. You don’t have business code yet. You just have the test. This is what TDD is all about: test first, business code later. Get the point?

To avoid the compilation error, we will code a separate unit (ChessPieces) and we will add it to the uses clause of our ChessPiecesTests unit.

unit ChessPieces;

interface

type
  TPiece = class
  private
  public
    function SetPosition(aX, aY: Integer): Boolean;
  end;

implementation

{ TPiece }

function TPiece.SetPosition(aX, aY: Integer): Boolean;
begin
end;

end.

Run the test again and now the compilation error is gone. Nonetheless, the test fails, because the Piece.SetPosition(4, 4) evaluates to False.

Let’s add the minimum business code possible to pass this test:

function TPiece.SetPosition(aX, aY: Integer): Boolean;
begin
  Result:= True;
end;

This passes the test. What? Yes, this passes the test, right?

OK, what now? Well, we keep adding new checks to the test and every time this happens, we need to add new business code in order to pass it. It is very important to add checks to test the boundaries of whatever we are trying to code. I think you are getting the point, so I will just add a bunch of checks at once:

procedure TPieceTest.SetPositionTest;
var
  Piece: TPiece;
begin
  Piece:= TPiece.Create;
  try
    //Test trivial (normal) workflow
    Check(Piece.SetPosition(4, 4) = True, '');

    //Tests boundaries
    Check(Piece.SetPosition(1, 1) = True, '');
    Check(Piece.SetPosition(1, 8) = True, '');
    Check(Piece.SetPosition(8, 1) = True, '');
    Check(Piece.SetPosition(8, 8) = True, '');

    //Test beyond the boundaries
    Check(Piece.SetPosition(3, 15) = False, '');
    Check(Piece.SetPosition(3, -15) = False, '');
    Check(Piece.SetPosition(15, 3) = False, '');
    Check(Piece.SetPosition(15, 15) = False, '');
    Check(Piece.SetPosition(15, -15) = False, '');
    Check(Piece.SetPosition(-15, 3) = False, '');
    Check(Piece.SetPosition(-15, 15) = False, '');
    Check(Piece.SetPosition(-15, -15) = False, '');
  finally
    Piece.Free;
end;

The test above is even checking for the attempts of positioning a piece outside the chess board.

To pass that test let’s write some business code:

function TPiece.SetPosition(aX, aY: Integer): Boolean;
begin
  Result:= True;
  if (aY < 1) or (aY > 8) then Result:= False
  else if (aX < 1) or (aX > 8) then Result:= False;
end;

Run the test and see how it passes.

The code above could be refactored or even rewritten. The tests will remain the same, allowing us to catch any bugs introduced with the code change.

For instance, we could write the procedure above as follows:

function TPiece.SetPosition(aX, aY: Integer): Boolean;
begin
  Result:= (aX > 0) and
           (aX < 9) and 
           (aY > 0) and
           (aY < 9);
end;

Run the test, and it will tell you if this refactoring (or reimplementation) works ok.

It’s important to note that a good test should cover all possible scenarios and workflows. Pay special attention to the boundaries. At this point, a good understanding of the requisites is indispensable.

Finally, more and more tests will be needed in a real world application. Each test will have its own checks. Each test will cover one piece of the functionality: this is what unit testing is intended for.

For further reading I recommend you Test Driven Development: By Example by Kent Beck. Check it out just below:

License

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

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About the Author

yanniel
Software Developer Digital Rapids
Canada Canada
My name is Yanniel Alvarez Alfonso. I was born in San Antonio de los Baños, Havana Province, Cuba on October 24th, 1982.
 
I majored in Information Technology Engineering at José Antonio Echeverría Polytechnic Institute (CUJAE) in Havana City, Cuba (July 2006). After that, I got a Masters Degree in Applied Computer Science at the same University (May 2009).
 
I used to work as a professor of Information Technology at CUJAE. Right now, I work as a Software Developer in Toronto, Canada. I moved to Canada under the Skilled Worker Program on February 26th, 2010.
 
This is my personal blog: Yanniel's notes; in which I write about miscellaneous topics.
 
The link at the end of this sentence compiles an index of all the articles I have written so far about Delphi Programming.

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