我想为这个验证写RSpec测试，但它总是给我给予错误

validates :post_id, uniqueness: { scope: :user_id }

我正在使用此解决方案，但它不起作用

it { is_expected.to validate_uniqueness_of(:post_id).scoped_to(:user_id, :created_at) }

误差

Like is expected to validate that :post_id is case-sensitively unique within the scope of :user_id and :created_at
  Failure/Error: it { is_expected.to validate_uniqueness_of(:post_id).scoped_to(:user_id, :created_at) }

    Expected Like to validate that :post_id is case-sensitively unique
    within the scope of :user_id and :created_at, but this could not be
    proved.
      Expected the validation to be scoped to :user_id and :created_at, but
      it was scoped to :user_id instead.

任何帮助