Merge pull request #312: Find the messages a refresh replaces through an index

Reviewed and merged by GPT on behalf of DHH.

test/models/message/pagination_test.rb

@@ -0,0 +1,16 @@
+require "test_helper"
+
+class Message::PaginationTest < ActiveSupport::TestCase
+  test "messages updated since a time are the newest page of them, in creation order" do
+    room = rooms(:watercooler)
+    first, second, third = room.messages.ordered.first(3)
+
+    travel 1.minute do
+      [ third, first, second ].each(&:touch)
+
+      stub_const(Message::Pagination, :PAGE_SIZE, 2) do
+        assert_equal [ second, third ], room.messages.page_updated_since(30.seconds.ago).to_a
+      end
+    end
+  end
+end