def METHOD_NAME(self):
    password = "password"
    user = factories.UserFactory(password=password)
    self.add_product_to_basket()
    page = self.get(reverse("checkout:index"))
    form = page.form
    form.select("options", GatewayForm.EXISTING)
    form["username"].value = user.email
    form["password"].value = password
    response = form.submit()
    self.assertRedirectsTo(response, "checkout:shipping-address")