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Re: [XP] TDD Quandary

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  • 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 1 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 2 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 3 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 4 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 5 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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