Make IDs more time-sortable in tests

In order for model ordering to work as expected in tests, we need to
keep two properties:

- Fixtures are all created in the past
- Models sort in the order that they were created

This allows us to do things like this:

    post cards_path, params: { ... }
    created_card = Card.last

When using UUIDv7 PKs rather than sequential integers, we have to make
sure a couple of things happen in order for this still to be true:

- Fixtures should generate deterministic IDs that translate to UUIDs
  that would have been created in the past (i.e. before today)
- Newly created objects must have enough precision in their timestamps
  so that they sort in the order they were created, and their random
  component doesn't come into play.

To solve this, we use the deterministic numeric ID as a number of
milliseconds after an early year. And we ensure that the new timestamps
we create have sub-millisecond precision.

test/controllers/boards/columns_controller_test.rb

@@ -16,7 +16,7 @@ class Boards::ColumnsControllerTest < ActionDispatch::IntegrationTest
       assert_response :success
     end
 
-    assert_equal "New Column", boards(:writebook).columns.order(created_at: :desc).first.name
+    assert_equal "New Column", boards(:writebook).columns.last.name
   end
 
   test "update" do

test/controllers/boards_controller_test.rb

@@ -20,7 +20,7 @@ class BoardsControllerTest < ActionDispatch::IntegrationTest
       post boards_path, params: { board: { name: "Remodel Punch List" } }
     end
 
-    board = Board.order(created_at: :desc).first
+    board = Board.last
     assert_redirected_to board_path(board)
     assert_includes board.users, users(:kevin)
     assert_equal "Remodel Punch List", board.name

test/controllers/cards/publishes_controller_test.rb

@@ -26,7 +26,7 @@ class Cards::PublishesControllerTest < ActionDispatch::IntegrationTest
       end
     end
 
-    new_card = Card.order(created_at: :desc).first
+    new_card = Card.last
     assert new_card.drafted?
     assert_redirected_to new_card
   end

test/controllers/cards_controller_test.rb

@@ -20,7 +20,7 @@ class CardsControllerTest < ActionDispatch::IntegrationTest
       post board_cards_path(boards(:writebook))
     end
 
-    card = Card.order(created_at: :desc).first
+    card = Card.last
     assert card.drafted?
     assert_redirected_to card
   end

test/controllers/filters_controller_test.rb

@@ -16,7 +16,7 @@ class FiltersControllerTest < ActionDispatch::IntegrationTest
     end
     assert_response :success
 
-    filter = Filter.order(created_at: :desc).first
+    filter = Filter.last
     assert_predicate filter.indexed_by, :closed?
     assert_predicate filter.assignment_status, :unassigned?
     assert_equal [ tags(:mobile) ], filter.tags

test/controllers/webhooks_controller_test.rb

@@ -35,7 +35,7 @@ class WebhooksControllerTest < ActionDispatch::IntegrationTest
       }
     end
 
-    webhook = Webhook.order(created_at: :desc).first
+    webhook = Webhook.last
 
     assert_redirected_to board_webhook_path(webhook.board, webhook)
     assert_equal board, webhook.board

test/models/card/closeable_test.rb

@@ -18,7 +18,7 @@ class Card::CloseableTest < ActiveSupport::TestCase
     end
 
     assert cards(:logo).closed?
-    assert cards(:logo).events.order(created_at: :desc).first.action.card_closed?
+    assert cards(:logo).events.last.action.card_closed?
     assert_equal users(:kevin), cards(:logo).closed_by
   end
 
@@ -29,6 +29,6 @@ class Card::CloseableTest < ActiveSupport::TestCase
       cards(:shipping).reopen
     end
     assert cards(:shipping).reload.open?
-    assert cards(:shipping).events.order(created_at: :desc).first.action.card_reopened?
+    assert cards(:shipping).events.last.action.card_reopened?
   end
 end

test/models/card/eventable/system_commenter_test.rb

@@ -45,7 +45,7 @@ class Card::Eventable::SystemCommenterTest < ActiveSupport::TestCase
     def assert_system_comment(expected_comment)
       assert_difference -> { @card.comments.count }, 1 do
         yield
-        comment = @card.comments.order(created_at: :desc).first
+        comment = @card.comments.last
         assert comment.creator.system?
         assert_match Regexp.new(expected_comment.strip, Regexp::IGNORECASE), comment.body.to_plain_text.strip
       end

test/models/card/postponable_test.rb

@@ -26,7 +26,7 @@ class Card::PostponableTest < ActiveSupport::TestCase
     end
 
     assert_equal users(:david), card.not_now.user
-    assert card.events.order(created_at: :desc).first.action.card_postponed?
+    assert card.events.last.action.card_postponed?
 
     assert_changes -> { card.reload.postponed? }, to: false do
       card.resume
@@ -42,7 +42,7 @@ class Card::PostponableTest < ActiveSupport::TestCase
       end
     end
 
-    assert card.events.order(created_at: :desc).first.action.card_auto_postponed?
+    assert card.events.last.action.card_auto_postponed?
   end
 
   test "scopes" do

test/models/card/statuses_test.rb

@@ -34,7 +34,7 @@ class Card::StatusesTest < ActiveSupport::TestCase
       @card = boards(:writebook).cards.create! creator: users(:kevin), title: "Published Card", status: :published
     end
 
-    event = Event.order(created_at: :desc).first
+    event = Event.last
     assert_equal @card, event.eventable
     assert_equal "card_published", event.action
   end
@@ -47,7 +47,7 @@ class Card::StatusesTest < ActiveSupport::TestCase
       card.publish
     end
 
-    event = Event.order(created_at: :desc).first
+    event = Event.last
     assert_equal card, event.eventable
     assert_equal "card_published", event.action
   end

test/models/card/taggable_test.rb

@@ -10,7 +10,7 @@ class Card::TaggableTest < ActiveSupport::TestCase
       @card.toggle_tag_with "ruby"
     end
 
-    assert_equal "ruby", @card.tags.order(created_at: :desc).first.title
+    assert_equal "ruby", @card.tags.last.title
 
     assert_difference -> { @card.tags.count }, -1 do
       @card.toggle_tag_with "ruby"

test/models/card_test.rb

@@ -23,7 +23,7 @@ class CardTest < ActiveSupport::TestCase
       cards(:logo).comments.create!(body: "Agreed.")
     end
 
-    assert_equal "Agreed.", cards(:logo).comments.order(created_at: :desc).first.body.to_plain_text.chomp
+    assert_equal "Agreed.", cards(:logo).comments.last.body.to_plain_text.chomp
   end
 
   test "assignment states" do
@@ -38,7 +38,7 @@ class CardTest < ActiveSupport::TestCase
       cards(:logo).toggle_assignment users(:kevin)
     end
     assert_not cards(:logo).assigned_to?(users(:kevin))
-    unassign_event = Event.order(created_at: :desc).first
+    unassign_event = Event.last
     assert_equal "card_unassigned", unassign_event.action
     assert_equal [ users(:kevin) ], unassign_event.assignees
 
@@ -46,7 +46,7 @@ class CardTest < ActiveSupport::TestCase
       cards(:logo).toggle_assignment users(:kevin)
     end
     assert cards(:logo).assigned_to?(users(:kevin))
-    assign_event = Event.order(created_at: :desc).first
+    assign_event = Event.last
     assert_equal "card_assigned", assign_event.action
     assert_equal [ users(:kevin) ], assign_event.assignees
   end

test/models/notifier/event_notifier_test.rb

@@ -39,7 +39,7 @@ class Notifier::EventNotifierTest < ActiveSupport::TestCase
 
     Notifier.for(events(:logo_published)).notify
 
-    assert_equal cards(:logo), Notification.order(created_at: :desc).first.source.eventable
+    assert_equal cards(:logo), Notification.last.source.eventable
   end
 
   test "assignment events only create a notification for the assignee" do

test/system/smoke_test.rb

@@ -40,7 +40,6 @@ class SmokeTest < ApplicationSystemTestCase
 
     notif = notifications(:logo_comment_david_mention_by_jz)
 
-    skip("Grouped notifications and the new UUID ids are making this test flaky")
     assert_selector "div##{dom_id(notif)}"
 
     within_window(open_new_window) { visit card_url(notif.card) }

test/test_helper.rb

@@ -94,19 +94,20 @@ module FixturesTestHelper
       # so that UUIDs sort in the same order as integer IDs
       fixture_int = Zlib.crc32("fixtures/#{label}") % (2**30 - 1)
 
-      # Use fixture_int as second offset from a fixed base time (1 year before 2025-01-01)
-      # This ensures all fixtures are in the past, and new test records are newest
+      # Translate the deterministic order into times in the past, so that records
+      # created during test runs are also always newer than the fixtures.
       base_time = Time.utc(2024, 1, 1, 0, 0, 0)
-      timestamp = base_time + fixture_int.seconds
+      timestamp = base_time + (fixture_int / 1000.0)
 
       uuid_v7_with_timestamp(timestamp, label)
     end
 
     def uuid_v7_with_timestamp(time, seed_string)
       # Generate UUIDv7 with custom timestamp and deterministic random bits
-      # Format: 48-bit timestamp_ms | 12-bit random | 4-bit version | 62-bit random
+      # Format: 48-bit timestamp_ms | 12-bit sub_ms_precision | 4-bit version | 62-bit random
 
-      timestamp_ms = (time.to_f * 1000).to_i
+      time_ms = time.to_f * 1000
+      timestamp_ms = time_ms.to_i
 
       # 48-bit timestamp (milliseconds since epoch)
       bytes = []
@@ -117,13 +118,18 @@ module FixturesTestHelper
       bytes[4] = (timestamp_ms >> 8) & 0xff
       bytes[5] = timestamp_ms & 0xff
 
-      # Derive deterministic "random" bits from seed_string
+      # Use the 12-bit rand_a field for sub-millisecond precision
+      # Extract fractional milliseconds and convert to 12-bit value (0-4095)
+      # This gives us ~0.244 microsecond precision
+      frac_ms = time_ms - timestamp_ms
+      sub_ms_precision = (frac_ms * 4096).to_i & 0xfff
+
+      # Derive deterministic "random" bits from seed_string for the remaining random bits
       hash = Digest::MD5.hexdigest(seed_string)
 
-      # 12-bit random + 4-bit version (0111 for v7)
-      rand_a = hash[0...3].to_i(16) & 0xfff
-      bytes[6] = ((rand_a >> 8) & 0x0f) | 0x70  # version 7
-      bytes[7] = rand_a & 0xff
+      # 12-bit sub-ms precision + 4-bit version (0111 for v7)
+      bytes[6] = ((sub_ms_precision >> 8) & 0x0f) | 0x70  # version 7
+      bytes[7] = sub_ms_precision & 0xff
 
       # 2-bit variant (10) + 62-bit random
       rand_b = hash[3...19].to_i(16) & ((2**62) - 1)