[gdal-dev] Intermittent failure with Python mocks

[Sean Gillies]

Hi Jon,

The number one gotcha with patching is documented here
https://docs.python.org/3/library/unittest.mock.html#where-to-patch. In a
nutshell, you have to patch your own module. I see you're patching gdal in
your tests. Patching gdal from your test doesn't do anything, it's too
late.

Hope this helps!

On Thu, Apr 13, 2023, 7:53 AM Jon Morris <Jon.Morris at jbarisk.com> wrote:

> I’m getting intermittent fails with our Python unit tests and I wondered
> if anyone has seen the same issue. I think it’s a race condition where a
> mock patch is either not applied at all or maybe applied too slowly so the
> patched function still has its original return value. It might be a pytest
> issue, but I’ve now seen it with two different GDAL methods so I’m just
> curious if anyone has any idea what may be going on.
>
>
>
> The first example I reported on Stack Overflow (
> https://stackoverflow.com/q/75185263/3182496) and looks something like
> this:
>
>
>
>         mock_feat_defn = mocker.patch.object(ogr.FeatureDefn,
> 'GetFieldCount')
>
>         mock_feat_defn.side_effect = RuntimeError("Some other error
> message")
>
>
>
>         with pytest.raises(RuntimeError, match="Some other error message"):
>
>             get_from_layer_schema(test_lyr, get_names=True,
> get_types=False)
>
>
>
> The second example is this:
>
>
>
>         with mock.patch('osgeo.gdal.Driver.Delete', side_effect=None):
>
>             with self.assertRaisesRegex(DatasetError, "Could not delete"):
>
>                 delete_path(shp_path)
>
>
>
> In both cases we’re mocking a GDAL method call to check one of our
> functions correctly raises an error, but sometimes it works and sometimes
> it doesn’t. If it’s not a GDAL issue, no problem, I will keep looking
> elsewhere for a solution.
>
>
>
> Jon
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