django/tests/admin_views/forms.py

from django.contrib.admin.forms import AdminAuthenticationForm
from django.contrib.admin.helpers import ActionForm
from django.core.exceptions import ValidationError


class CustomAdminAuthenticationForm(AdminAuthenticationForm):
    class Media:
        css = {"all": ("path/to/media.css",)}

    def clean_username(self):
        username = self.cleaned_data.get("username")
        if username == "customform":
            raise ValidationError("custom form error")
        return username


class MediaActionForm(ActionForm):
    class Media:
        js = ["path/to/media.js"]