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Re: TDD Quandary

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  • Ken Boucher
    ... What strikes me as painful about this is tt seems that the tests involved are mostly testing Direct X, not your code, and as far as that goes, they re only
    Message 1 of 10 , Oct 2, 2004
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      > How in the world do I test drive graphics (DirectX) code. That is,
      > code that really does very little data manipulation at all, but
      > basically just works with an API to get things done. And by done, I
      > mean drawing objects on the screen.

      What strikes me as painful about this is tt seems that the tests
      involved are mostly testing Direct X, not your code, and as far as
      that goes, they're only testing how the version of Direct-X you have
      installed on that machine actually works. It makes me wonder if TDD
      is the right tool for that particular problem or if you want a different
      tool for that layer.

      Software tools that may help:
      http://www.parasoft.com/jsp/products/article.jsp?articleId=1500 for C++
      http://www.mvps.org/directx/smalltalk/articles/startmtdx8.htm for smalltalk
    • Ron Jeffries
      ... Good questions, Laurent [and Erik]. This will help us decide which tests are necessary. TDD, as I do it, is for testing the logic of my program. What s
      Message 2 of 10 , Oct 2, 2004
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        On Saturday, October 2, 2004, at 6:41:48 AM, Laurent Bossavit wrote:

        >> How in the world do I test drive graphics (DirectX) code.

        > When such code is buggy, in exactly what ways does it tend to be
        > broken ? How can you tell ?

        Good questions, Laurent [and Erik]. This will help us decide which tests
        are necessary.

        TDD, as I do it, is for testing the "logic" of my program. What's the logic
        of the programs you are writing, Erik?

        Ron Jeffries
        www.XProgramming.com
        This is how I develop software.
        Take the parts that make sense to you.
        Ignore the rest.
      • Phlip
        ... Write a temporary test function called reveal() . It will activate the MS Windows event queue, and allow a testee to paint on the screen, and stay up
        Message 3 of 10 , Oct 2, 2004
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          bigbaseballer wrote:

          > How in the world do I test drive graphics (DirectX)
          > code. That is,
          > code that really does very little data manipulation
          > at all, but
          > basically just works with an API to get things done.
          > And by done, I
          > mean drawing objects on the screen. Not something I
          > can really "test"
          > in the sense of having inputs and outputs and
          > verifying them, it is
          > just so complex that the closest thing to
          > traditional unit testing I
          > could do is verify if certain pixels were certain
          > colors ... and I
          > assure you that would be a worthless test.

          Write a temporary test function called 'reveal()'. It
          will activate the MS Windows event queue, and allow a
          testee to paint on the screen, and stay up until you
          close it.

          Call it at the bottom of your test case. The case will
          set up a scenario, then each time you hit the test
          button a window appears, and you can visually inspect
          the results. When you like the appearance, comment out
          the 'reveal()'.

          Sadly, this technique boosts early velocity, and
          without real assertions in your code the technique
          will lead to source cannot refactor without high risk.

          > The idea of mock objects comes up. Except, that idea
          > has two
          > implications. First of all, it means that I need to
          > mock the DirectX
          > API ... which I could do. It would be a bit
          > annoying, but I could do
          > it.

          The style is called "Mock Graphics", and one should
          use it as a last resort.

          I recently wrote an OpenGL application using Mock
          Graphics directly at the OpenGL boundary, based on the
          glTrace package by Phil Frisbie, Jr. (When Kent Beck
          finishes reviewing this effort, I might get to publish
          it...)

          The unwisely curious can get the sample code early, in
          the CVS repository at http://sf.net/projects/flea

          > But my BIGGEST issue with this approach is
          > this: I have
          > historically test driven a public interface, and
          > then refactored some
          > internal stuff. But basically, the test shows how
          > the code is supposed
          > to work from an external viewpoint. I get complete
          > code coverage this
          > way, and from talking to some people it sounds like
          > I am on the right
          > track. But what about this? My external interface is
          > not supposed to
          > really tell anything about the DirectX api. How do
          > mocks come into
          > play when I can't actually put them into use without
          > making the
          > interface aware of DirectX?

          Here is a "does this help?" answer: Copy your code
          into a scratch sandbox project, outside your version
          control system, and then do Exploratory Testing and
          Spike Solutions in it. Those are big words for "noodle
          around". Make the code do what you want, and neglect
          the tests. Then write beautiful tests that look like
          they somehow came before the tested code.

          Then copy the tests, line by line, back into the main
          project, and use them to truly test-first the design
          your scratch project arrived at.


          =====
          Phlip
          http://industrialxp.org/community/bin/view/Main/TestFirstUserInterfaces



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        • bigbaseballer
          ... the logic ... Ok, to the first question, buggy would be either a) it crashes, or b) there are visual artifacts that we don t like. That second one is sort
          Message 4 of 10 , Oct 2, 2004
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            --- In extremeprogramming@yahoogroups.com, Ron Jeffries
            <ronjeffries@X...> wrote:
            > On Saturday, October 2, 2004, at 6:41:48 AM, Laurent Bossavit wrote:
            >
            > >> How in the world do I test drive graphics (DirectX) code.
            >
            > > When such code is buggy, in exactly what ways does it tend to be
            > > broken ? How can you tell ?
            >
            > Good questions, Laurent [and Erik]. This will help us decide which tests
            > are necessary.
            >
            > TDD, as I do it, is for testing the "logic" of my program. What's
            the logic
            > of the programs you are writing, Erik?

            Ok, to the first question, buggy would be either a) it crashes, or b)
            there are visual artifacts that we don't like. That second one is sort
            of broad ... but really that kind of comes down to acceptance testing
            rather than unit testing.

            And there is logic in this part of the code, I need to manage the
            DirectX state, and how I actually draw certain things. But other than
            managing DirectX, most of the actual logic is in performance
            optimizations, and I am looking to stay away from that (for now). But
            when I start, I want to have something to fallback on.

            I think I will do what Philip said. It is actually a really good idea,
            under the circumstances ... I really think I could write decent tests
            if I knew exactly what I was doing, versus just knowing what I want
            the end result to be.
          • Laurent Bossavit
            Erik, ... I would think unit-testing-at-all would be sufficient to catch most of these ? Or is there something else I should know about the kind of DirectX
            Message 5 of 10 , Oct 2, 2004
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              Erik,

              > Ok, to the first question, buggy would be either a) it crashes,

              I would think unit-testing-at-all would be sufficient to catch most
              of these ? Or is there something else I should know about the kind of
              DirectX coding errors, specifically, that make it crash ?

              > b) there are visual artifacts that we don't like.

              Can you recall a specific occasion where you had written code that
              produced a visual artifact, and the code should have been written
              another way ?

              Cheers,

              -[Laurent]-
              The greatest obstacle to transforming the world is that we lack the
              clarity and imagination to conceive that it could be different.
              Roberto Mangabeira Unger
            • J. B. Rainsberger
              ... I might use the Gold Master technique here. Draw the screen and check it by hand once. Now capture it and check future draws against the output you
              Message 6 of 10 , Oct 2, 2004
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                bigbaseballer wrote:

                > How in the world do I test drive graphics (DirectX) code. That is,
                > code that really does very little data manipulation at all, but
                > basically just works with an API to get things done. And by done, I
                > mean drawing objects on the screen. Not something I can really "test"
                > in the sense of having inputs and outputs and verifying them, it is
                > just so complex that the closest thing to traditional unit testing I
                > could do is verify if certain pixels were certain colors ... and I
                > assure you that would be a worthless test.

                I might use the Gold Master technique here. Draw the screen and check it
                by hand once. Now capture it and check future draws against the output
                you verified by hand. If a future draw is different from the Gold
                Master, the test fails. Time to investigate. It's not TDD, but it
                provides a refactoring safety net.

                Another technique is to think of driving the DirectX API as generating a
                sequence of events that a DirectXEventListener catches and sends to the
                API. The techniques for testing event sources and event listeners are
                well documented. (See _JUnit Recipes_, chapter 14.) Now the goal is to
                verify that your code generates the proper set (or sequence) of events,
                the result of which would be a correctly-drawn screen. The set of events
                could be quite big. If it is, then I highly recommend testing this with
                FIT/FitNesse, rather than xUnit.

                I hope this helps.
                --
                J. B. (Joe) Rainsberger
                Diaspar Software Services
                http://www.diasparsoftware.com :: +1 416 791-8603
                Predictable, repeatable, quality delivery
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