"""

Make sure that the content type cache (see ContentTypeManager) works correctly.

Lookups for a particular content type -- by model or by ID -- should hit the

database only on the first lookup.

First, let's make sure we're dealing with a blank slate (and that DEBUG is on so

that queries get logged)::

    >>> from django.conf import settings

    >>> settings.DEBUG = True

    >>> from django.contrib.contenttypes.models import ContentType

    >>> ContentType.objects.clear_cache()

    >>> from django import db

    >>> db.reset_queries()

At this point, a lookup for a ContentType should hit the DB::

    >>> ContentType.objects.get_for_model(ContentType)

    <ContentType: content type>

    >>> len(db.connection.queries)

    1

A second hit, though, won't hit the DB, nor will a lookup by ID::

    >>> ct = ContentType.objects.get_for_model(ContentType)

    >>> len(db.connection.queries)

    1

    >>> ContentType.objects.get_for_id(ct.id)

    <ContentType: content type>

    >>> len(db.connection.queries)

    1

Once we clear the cache, another lookup will again hit the DB::

    >>> ContentType.objects.clear_cache()

    >>> ContentType.objects.get_for_model(ContentType)

    <ContentType: content type>

    >>> len(db.connection.queries)

    2

Don't forget to reset DEBUG!

    >>> settings.DEBUG = False

"""