Add unit tests for EntryPresenter
user
```ruby
require 'spec_helper'

RSpec.describe EntryPresenter do
  describe '#summary' do
    let(:document) {
      FactoryBot.build(:document, description: 'This is the summary. And this is extra.')
    }
    it 'displays the truncated description' do
      expect(EntryPresenter.new(document, true).summary).to eq('This is the summary.')
    end
    it 'returns nil' do
      expect(EntryPresenter.new(document, false).summary).to be nil
    end
  end
  describe '#tag' do
    it 'returns a tag' do
      document = FactoryBot.build(:document, link: '/path/to/content')
      atom_feed_builder = ActionView::Helpers::AtomFeedHelper::AtomFeedBuilder.new(nil, nil, schema_date: 2019)
      expect(EntryPresenter.new(document, true).tag(atom_feed_builder)).to eq('tag:www.test.gov.uk,2019:/path/to/content')
    end
  end
  describe '#updated_at' do
    it 'returns the public timestamp' do
      document = FactoryBot.build(:document, public_timestamp: "Thu Nov 29 14:33:20 2001", release_timestamp: "Thu Nov 29 14:33:20 2010")
      expect(EntryPresenter.new(document, true).updated_at).to eq("Thu Nov 29 14:33:20 2001")
    end
    it 'returns the release timestamp' do
      document = FactoryBot.build(:document, public_timestamp: nil, release_timestamp: "Thu Nov 29 14:33:20 2010")
      expect(EntryPresenter.new(document, true).updated_at).to eq("Thu Nov 29 14:33:20 2010")
    end
  end
  describe '#feed_ended_id' do
    it 'returns a feed_ended_id' do
      atom_feed_builder = ActionView::Helpers::AtomFeedHelper::AtomFeedBuilder.new(nil, nil, schema_date: 2019)
      expect(EntryPresenter.feed_ended_id(atom_feed_builder, '/path/to/content')).to eq('tag:www.test.gov.uk,2019:/path/to/content/feed-ended')
    end
  end
end
```
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