gunittest: update module interface doctest

[nilason]

Adapts documentation to the addition of 'weighting_function' parameter to 'r.neighbors' introduced with 20f370c (#597).

Unit tests fails with errors like:

FAIL: Module (grass.pygrass.modules.interface.module)
Doctest: grass.pygrass.modules.interface.module.Module
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/Library/Frameworks/Python.framework/Versions/3.9/lib/python3.9/doctest.py", line 2204, in runTest
    raise self.failureException(self.format_failure(new.getvalue()))
AssertionError: Failed doctest test for grass.pygrass.modules.interface.module.Module
  File "/Volumes/dev/grass/dist.x86_64-apple-darwin19.6.0/etc/python/grass/pygrass/modules/interface/module.py", line 323, in Module

----------------------------------------------------------------------
File "/Volumes/dev/grass/dist.x86_64-apple-darwin19.6.0/etc/python/grass/pygrass/modules/interface/module.py", line 350, in grass.pygrass.modules.interface.module.Module
Failed example:
    neighbors.get_bash()
Expected:
    'r.neighbors input=mapA method=average size=5 quantile=0.5 output=mapB'
Got:
    'r.neighbors input=mapA size=5 method=average weighting_function=none quantile=0.5 output=mapB'

[ninsbl]

Thanks @nilason for catching this. What is surprising is that weighting_function is not a required option:

grass/raster/r.neighbors/main.c

Line 226 in 3293018

parm.weighting_function->required = NO;

There seems to be a simmilar issue here:
#1158 (comment)
where @wenzeslaus suggests that the issue is probably with the pygrass module interface and not the test...

[nilason]

Thanks @nilason for catching this. What is surprising is that weighting_function is not a required option:

grass/raster/r.neighbors/main.c

Line 226 in 3293018

parm.weighting_function->required = NO;

There seems to be a simmilar issue here:
#1158 (comment)
where @wenzeslaus suggests that the issue is probably with the pygrass module interface and not the test...

I don't know the code behind the tests well enough yet, but I note method:

grass/raster/r.neighbors/main.c

Line 208 in 3293018

parm.method->required = NO;

is neither required, yet present.

[nilason]

However both method and weighting_function have default value (->answer = ...).

[ninsbl]

However both method and weighting_function have default value (->answer = ...).

Right. I overlooked that the tests checks the constructed bash command... Makes sense.

[wenzeslaus]

Handling of "not required" with default value is strange, but that's all I can say about it.

[nilason]

Handling of "not required" with default value is strange, but that's all I can say about it.

At first glance, yes, but remember "required" is meant for parameter(s) required for the user's command. I'd say a required parameter with a default would be strange.