Adding new tests to increase coverage

No, that doesn't work with numpy
On Wed, Oct 29, 2014 at 8:16 PM Dan Blanchard <notifications@github.com>
wrote:

> In skll/data/featureset.py:
>
> > @@ -221,7 +222,8 @@ def filter(self, ids=None, classes=None, features=None, inverse=False):
> >                                             feat_name.split('=', 1)[0] in
> >                                             features)}))
> >              if inverse:
> > -                columns = ~columns
> > +                all_columns = np.arange(self.features.shape[1])
>
> ~columns didn't work here?
>
> —
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> <https://github.com/EducationalTestingService/skll/pull/191/files#r19581641>
> .
>