Add minimal test on rss feed response (#17221)

* Add minimal test on rss feed response

* Update date to string conversion to avoid deprecation

It wouldn't make sense to use a deprecated method here.

spec/requests/articles/articles_feed_spec.rb

@@ -0,0 +1,12 @@
+require "rails_helper"
+
+RSpec.describe "ArticlesFeed", type: :request do
+  let!(:article) { create(:article) }
+
+  it "returns an rss feed with published articles" do
+    get "/feed"
+
+    expect(response.body).to include(article.title)
+    expect(response.body).to include("<pubDate>#{article.published_at.to_fs(:rfc822)}</pubDate>")
+  end
+end