'Test prefix can be set (see #18872)'

def test_get_prefix(self):

    test_string = 'test'
    rf = RequestFactory()
    get_request = rf.get('/')
    class TestFormMixin(FormMixin, ):
        request = get_request
    default_kwargs = TestFormMixin().get_form_kwargs()
    self.assertEqual(None, default_kwargs.get('prefix'))
    set_mixin = TestFormMixin()
    set_mixin.prefix = test_string
    set_kwargs = set_mixin.get_form_kwargs()
    self.assertEqual(test_string, set_kwargs.get('prefix'))
