Check that ValidationError is actually the one I expect in a test

I have a test which creates a Django object "forgetting" to set one field. It should fail, so I check:

p = Person.objects.create(name='test') 
self.assertRaises(ValidationError, p.full_clean)

The forgotten field is birth_date, so if I intercepted the exception and printed it, the error would be:

{'birth_date': ['This field cannot be blank.']}` 

Now I added another field to Person, which also shouldn't be left blank. The error now would be:

{'birth_date': ['This field cannot be blank.'], 'category': ['This field cannot be blank.']}

With the above code, I silently suppress both errors. I need to test that the code raises a specific validation error. Is there a good way to do it? For now I've this workaround:

try:
    p.full_clean()
except ValidationError as e:
    self.assertIn('birth_date', dict(e))
    self.assertEqual(len(dict(e).keys()), 1, msg="Expected one error, found more")

But if there could have been two different errors with 'birth_date', this would catch either.

Is there a better way?