[py-dev] py.test generative tests unexpected behavior

[Jim.Vickroy at noaa.gov]

----- Original Message -----
From: Carl Friedrich Bolz <cfbolz at gmx.de>
Date: Monday, December 17, 2007 8:25 am
Subject: Re: [py-dev] py.test generative tests unexpected behavior

> Hi!
> 
> j. vickroy wrote:
> [snip]
> > The attached file (py-test-generator-trial.py) demonstrates a 
> behavior I 
> > do not understand.
> [snip]
> 
> I don't know generative test semantics all that well, I hoped 
> somebody 
> else would answer this. However, my theory is as follows:
> 
> py.test first collects all the results of the generator and then 
> runs 
> them all. Since your test keeps global state, the state is already 
> changed when the first test is run. To me this sounds like 
> reasonable 
> behavior, global state is not good in tests anyway.
> 
> Does that make things clearer?
> 
> Cheers,
> 
> Carl Friedrich
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> py-dev at codespeak.net
> http://codespeak.net/mailman/listinfo/py-dev
> 

Thanks, Carl.

I do understand (at least) some of the pitfalls of global state and I do
*almost always* avoid using it.  However, in this case, I am having
difficulty seeing why it is responsible for the observed behavior.

Having said that, prior to using the global *image* object, I tried to
use the setup_module(module) function to define the *image* object but
was unable to determine how to reference it in the test function.  The
global *image* object was a crude work-around.

Can you offer some suggestions on how I should have proceeded given that
I really do not need to create a new *image* object for each test.

Thanks again,
-- jv