As far as I can tell, it's not possible to use assertFormSetError, because
the key required to get at the formset is technically
"inline_admin_formset.formset",
and assertFormError and assertFormsetError do not currently support dot
notation expansion, unlike templates (
http://osdir.com/ml/python-django-user/2008-02/msg01627.html). I have,
however, added a little more comments and details to clarify what the tests
are doing. Please let me know if there is another way to get at the formset
that I'm overlooking.

In response to your first comment regarding whether this is a regression
test, the bug is about making sure that validation runs in the formset if
parent form fails validation. The test demonstrates this, and it did fail
the first time I wrote it before I fixed the bug (and I demonstrated
toEvilDMP at the sprints that it failed under the old code [at the time],
and passed under the new code). The bug is not about whether validation
passes in the child form when the parent form is invalid (in fact timo
implied in his comments to the ticket that this might not be the case if
the child form validates against parent datetimes); it's also not about
child form validation passing when parent validation passes. Is it possible
that I'm misunderstanding your objection regarding what isn't being tested?