formsetで少なくとも１つは入力させるためのチェック

forms.py

# coding=utf-8
from django import forms


class PersonForm(forms.Form):
    name = forms.CharField()
    age = forms.IntegerField()


class AtLeastOneFormRequiredBaseFormSet(forms.formsets.BaseFormSet):
    at_least_on_form_required_error = u"少なくとも１つは入力してください"

    def clean(self):
        if not getattr(self.forms[0], "cleaned_data"):
            raise forms.ValidationError(self.at_least_on_form_required_error)


PersonFormSet = forms.formsets.formset_factory(PersonForm,
                                               extra=2,
                                               formset=AtLeastOneFormRequiredBaseFormSet)

test_forms.py

# coding=utf-8
from django.test import TestCase
from .forms import PersonFormSet


class PersonFormSetTest(TestCase):
    def test_at_least_one_form_required(self):
        data = {
            'form-TOTAL_FORMS': '2',
            'form-INITIAL_FORMS': '2',
            'form-MAX_NUM_FORMS': '',
            'form-0-age': '',
            'form-0-name': '',
            'form-1-age': '',
            'form-1-name': '',
        }

        f = PersonFormSet(data)
        self.assertTrue(f.is_bound)
        self.assertFalse(f.is_valid())
        self.assertEquals(f.non_form_errors()[0], f.at_least_on_form_required_error)