discourse/spec/system/post_stream_spec.rb

# frozen_string_literal: true

describe "Post stream", type: :system do
  fab!(:topic)
  fab!(:user)
  fab!(:posts) { Fabricate.times(20, :post, topic: topic) }

  before do
    sign_in(user)
    SiteSetting.glimmer_post_stream_mode = "enabled"
  end

  it "cloaks posts that are far from the viewport" do
    # Visit the topic page
    visit "/t/#{topic.slug}/#{topic.id}/1"

    # Ensure there are visible posts
    expect(page).to have_css(".topic-post")

    post_stream = find(".post-stream")

    # Ensure the first post is uncloaked
    expect(post_stream).to have_css("> [data-post-number='1']")
    expect(post_stream).to have_no_css("> [data-post-number='1'].post-stream--cloaked")

    # Check that some posts are cloaked (not all posts should be fully rendered at once)
    # The posts that are far from the viewport should have the "post-stream--cloaked" class
    expect(post_stream).to have_css(".post-stream--cloaked")

    # Get the number of the last post
    last_post_number = topic.highest_post_number

    # Scroll to the bottom of the page to load more posts
    # We use the :end key to scroll to the bottom
    send_keys(:end)

    # Verify that the last post is not cloaked
    expect(post_stream).to have_no_css(
      "> [data-post-number='#{last_post_number}'].post-stream--cloaked",
    )

    # Verify that some posts at the top are now cloaked
    # we can check the first post to see if it's cloaked
    expect(post_stream).to have_css("> [data-post-number='1'].post-stream--cloaked")
  end
end