Ruby on rails Rails在数据库关联表中对唯一性的测试

每个用户都可以通过：：active\u vote\u relationships为一篇文章投票，该文章由一个关联建模：每个用户

都有\u many:voting。他们应该只被允许投票一次，所以我在模式中得到了
unique:true
：

add_index "voterelationships", ["voter_id", "voted_id"], name: "index_voterelationships_on_voter_id_and_voted_id", unique: true, using: :btree

我试图通过让用户投票给他已经投票支持的帖子来测试这一点：

test "shouldn't be able to vote again for a post already voted for" do
  assert_no_difference '@user.postvoting.count' do
    xhr :post, voterelationships_path(voter_callsign: @user.callsign, voted_id: @post_1.id)
  end
end

我期待着考试通过。相反，我得到了以下错误：

ActiveRecord::RecordNotUnique: PG::UniqueViolation: ERROR:  duplicate key value violates unique constraint "index_voterelationships_on_voter_id_and_voted_id"

唯一性要求似乎正确地防止了表中的重复对，但为什么这会导致测试错误而不是通过？我以为第二次投票会被数据库拒绝。如何通过考试？
这是正常的。您应该使用
assert\u raises
来断言将引发
ActiveRecord:：RecordNotUnique
异常

例如：

assert_raises ActiveRecord::RecordNotUnique do
  xhr :post, voterelationships_path(voter_callsign: @user.callsign, voted_id: @post_1.id)
end