py.test generative tests behavior unexpected

[Jim Vickroy]

Hello all,

I'm a first time user of py.tests.

My setup is:
* py.test v0.9.0
* Python 2.5 (r25:51908, Sep 19 2006, 09:52:17) [MSC v.1310 32 bit 
(Intel)] on win32
* Microsoft Windows XP Pro (service pack 2)

The attached file (py-test-generator-trial.py) demonstrates a behavior I 
do not understand.

When test_filters() is implemented as a generator, the tests appear to 
be run twice and all tests fail during the second iteration except for 
the final case ('AL12_1','Gray') in the loop.

When the yield statement, in test_filters(), is disabled and the 
assertion statement is enabled, the behavior is as expected -- namely 
the tests are performed once and all pass.

Could someone help me to understand this behavior?

Thanks,
--jv

P.S.
I could provide captured output if that is helpful.
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