Natural naming warning in unit tests

[avalentino]

.....................Exception AttributeError: AttributeError("'File' object has no attribute 
'_node_manager'",) in ................................................./home/antonio/projects
/PyTables/build/lib.linux-x86_64-3.3/tables/path.py:100: NaturalNameWarning: object 
name is not a valid Python identifier: 'test_filenode.dat'; it does not match the pattern 
``^[a-zA-Z_][a-zA-Z0-9_]*$``; you will not be able to use natural naming to access this 
object; using ``getattr()`` will still work, though
  NaturalNameWarning)
..

The problem seems to be originated in tables/nodes/tests/test_filenode.py DirectReadWriteTestCase.

See also #342.

[avalentino]

@andreas-h, @scopatz any idea on how to fix this?
Change the naming policy (e.g. filename.ext --> filename_ext) or just silence the warning?

[scopatz]

Can we just change the filename? Or the group / array in the file?

[scopatz]

I don't think that we should change or supress the warning.

[avalentino]

Can we just change the filename?

Do you mean the name of the file used for the test?

Or the group / array in the file?

Probably this is the best option.
We just need a rule to translate file names into array/group names.
The original filename/path could be saved as attribute somewhere.

I don't think that we should change or supress the warning.

+1