RSpec集合是否包含空数组？

我在Post模型中有一个搜索方法：

def self.search(search, category_id)
  if search.strip.empty?
    []
  elsif category_id.empty?
    Post.approved.where('lower(title) LIKE ?', "%#{search.downcase.strip}%")
  else
    @category = Category.find_by('id = ?', category_id.to_i)
    @category.posts.approved.where('lower(title) LIKE ?', "%#{search.downcase.strip}%")
  end
end

这是我的post_spec.rb文件

require 'rails_helper'

RSpec.describe Post, type: :model do
  let(:user) { create(:user) }
  let(:category) { create(:category) }
  let(:comments) { create(:comment) }
  let(:likes) { create(:like) }
 
 describe 'methods' do
    describe 'search post by keyword or by category' do
      let(:post_1) { create(:post, title: 'some example title') }
      let(:post_2) { create(:post, title: 'another example title') }
     
      it 'return post with title like keyword' do
        expect(described_class.search('example', category.id.to_s)).to contain_exactly(post_1)
        expect(described_class.search('EXAMPLE', category.id.to_s)).to contain_exactly(post_1)
        expect(described_class.search('title', category.id.to_s)).to contain_exactly(post_1, post_2)
        expect(described_class.search('foo', category.id.to_s)).to be_empty
      end
    end
  end
end

我不知道为什么我的实际收集是一个空数组，而不是帖子

1) Post methods search post by keyword or by category return post with title like keyword
     Failure/Error: expect(described_class.search('example', category.id.to_s)).to contain_exactly(post_1)
     
       expected collection contained:  [#<Post id: 152, title: "some example title"]
       actual collection contained:    []
       the missing elements were:      [#<Post id: 152, title: "some example title"]

1）Post方法按关键字或类别搜索Post返回具有类似标题的关键字的Post
失败/错误：期望（描述的类搜索（'example'，category.id.to_））。准确地包含（post_1）
预期收集包含：[#