[PyOpenGL-Users] Re: Test-first and mock objects with PyOpenGL

[Mike C. F. <mcf...@ro...>]

I've never done unit testing with OpenGL code, but I'll give a shot at 
the problem.

I'd guess the easiest test you could create would be to create an image 
that shows what you want and simply test whether that matches the image 
created by the new system.  Problem there is that the original image 
would need to be generated by your system, so you'd have that 
anti-pattern (don't recall what the XP name is) where you rely on output 
of the system to check correctness of the system.

If you really want to make the checks "manually predicted", you'd have 
to figure out particularly what calls, with what parameters you expected 
to get... all in all, sounds like a pain in the arse unless you're 
dropping in the "mockup" with the "known-good" system to generate a set 
of data... that's the same anti-pattern cropping up though.

 From a practical standpoint, replacing the whole GL with a mock-up 
seems a bit extreme (you'd have to figure out the internal state to do 
it right I'd think).  You could easily write a script that just walks 
through the Python OpenGL.GL, OpenGL.GLU and OpenGL.GLUT modules 
replacing every method with a wrapped version which logs the method 
name, parameters and return values to somewhere.  Check that log versus 
your expected results and you'd be golden (assuming you can create the 
set of "expected results" somehow).  Tarn did something very similar a 
while back to introduce stronger error checking without changing the C code.

Well, hope that helps somewhat, shout if anything I've said is unclear,
Mike

Phlip wrote:
> Alpha OpenGL Engineers:
> 
> I have a large spike-solution ("quicky non-production quality code
> base") of PyOpenGL, and I want to refactor it into something healthy.
> 
> I don't want to use GuruChecksOutput. This means I want tests that
> reveal changes did not affect how the code call the GL libraries.
> 
> The standard way to do this is to provide a MockObject in place of
> something, call the tested functions, let them call into the
> MockObject, and test what they told it. If these values did not change
> then the refactor did not break anything important.
> 
> However, I don't know if I have to Mock GL itself. Maybe I can replace
> OpenGL's back-end with a Mock that renders not to the screen but into
> my test code.
> 
> Who has done this and knows the pattern for it?
> 


-- 
_______________________________________
   Mike C. Fletcher
   http://members.rogers.com/mcfletch/