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"""
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
"""
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