'formfield_overrides works for a custom field class.'

def test_formfield_overrides_for_custom_field(self):

    class AlbumAdmin(admin.ModelAdmin, ):
        formfield_overrides = {MyFileField: {'widget': forms.TextInput()}}
    ma = AlbumAdmin(Member, admin.site)
    f1 = ma.formfield_for_dbfield(Album._meta.get_field('backside_art'), request=None)
    self.assertIsInstance(f1.widget, forms.TextInput)
