Add Query mock to MockSet

[nfantone]

Mock QuerySet.query by means of a MagicMock following the sql.Query spec.

This makes it so attributes from QuerySet.query behave as expected, including callable properties.

As an example, the following currently breaks:

from django.db.models import Subquery

ms = MockSet()

Subquery(ms.only("field"))
# Raises TypeError: 'NoneType' object is not callable

This is due to the Subquery constructor trying to call query.clone() on the given QuerySet.

class Subquery(BaseExpression, Combinable):
    # ...

    def __init__(self, queryset, output_field=None, **extra):
        # Allow the usage of both QuerySet and sql.Query objects.
        self.query = getattr(queryset, "query", queryset).clone()

[stefan6419846]

Thanks for your PR. Could you please add corresponding tests as well?

If I understand #182 correctly, this will add some further breakage? In this case, we probably should look for a fix first.

[nfantone]

@stefan6419846 I'm not sure if this is the right approach, if I'm being honest. My goal was to add support for Subquery but, ultimately, couldn't make it work.

AFAICT, changes from this PR wouldn't break anything (CI complains about flake8 formatting).

Let's continue the discussion in #182 and we can, then, revisit this.