def METHOD_NAME(app: Application):
    patch_babel(app)
    # use 'en': short date pattern is 'M/d/yy'
    headers = {"Accept-Language": "en"}
    with app.test_request_context(headers=headers):
        field = fields.DateField().bind(Form(), "dt")
        field.data = datetime.date(2011, 1, 23)
        assert field._value() == "1/23/2011"