From https://once.com/writebook

test/models/leaf/positionable_test.rb

@@ -0,0 +1,96 @@
+require "test_helper"
+
+class Leaf::PositionableTest < ActiveSupport::TestCase
+  setup do
+    @leaves = books(:handbook).leaves.positioned
+  end
+
+  test "items are sorted in positioned order" do
+    assert_equal [ leaves(:welcome_section), leaves(:welcome_page), leaves(:summary_page), leaves(:reading_picture) ], @leaves
+  end
+
+  test "items can be moved earlier" do
+    leaves(:welcome_page).move_to_position(0)
+
+    assert_equal [ leaves(:welcome_page), leaves(:welcome_section), leaves(:summary_page), leaves(:reading_picture) ], @leaves.reload
+  end
+
+  test "items can be moved beyond the start, which puts them at the start" do
+    leaves(:welcome_page).move_to_position(-99)
+
+    assert_equal [ leaves(:welcome_page), leaves(:welcome_section), leaves(:summary_page), leaves(:reading_picture) ], @leaves.reload
+  end
+
+  test "items can be moved later" do
+    leaves(:welcome_section).move_to_position(2)
+
+    assert_equal [ leaves(:welcome_page), leaves(:summary_page), leaves(:welcome_section), leaves(:reading_picture) ], @leaves.reload
+  end
+
+  test "items can be moved beyond the end, which puts them at the end" do
+    leaves(:welcome_section).move_to_position(99)
+
+    assert_equal [ leaves(:welcome_page), leaves(:summary_page), leaves(:reading_picture), leaves(:welcome_section) ], @leaves.reload
+  end
+
+  test "items can be moved to their existing position" do
+    leaves(:welcome_page).move_to_position(1)
+
+    assert_equal [ leaves(:welcome_section), leaves(:welcome_page), leaves(:summary_page), leaves(:reading_picture) ], @leaves.reload
+  end
+
+  test "items can be moved in blocks" do
+    leaves(:welcome_section).move_to_position(1, followed_by: [ leaves(:welcome_page), leaves(:summary_page) ])
+
+    assert_equal [ leaves(:reading_picture), leaves(:welcome_section), leaves(:welcome_page), leaves(:summary_page) ], @leaves.reload
+  end
+
+  test "new items are inserted at the end" do
+    new_page = books(:handbook).press Page.new(body: "New Page"), title: "New Page"
+
+    assert_equal new_page, books(:handbook).leaves.positioned.last
+  end
+
+  test "the first item in the collection has the expected score" do
+    books(:handbook).leaves.destroy_all
+    new_page = books(:handbook).press Page.new(body: "New Page"), title: "New Page"
+
+    assert_equal 1, new_page.position_score
+  end
+
+  test "positioning is rebalanced when necessary" do
+    leaves(:welcome_section).update!(position_score: 1e-11)
+    leaves(:welcome_page).update!(position_score: 2e-11)
+
+    leaves(:summary_page).move_to_position(1)
+
+    assert_equal leaves(:summary_page), @leaves.reload.second
+    assert_equal [ 1, 2, 3, 4 ], @leaves.pluck(:position_score)
+  end
+
+  test "items know their neighbours" do
+    assert_equal leaves(:welcome_section), leaves(:welcome_page).previous
+    assert_equal leaves(:summary_page), leaves(:welcome_page).next
+
+    assert_nil leaves(:welcome_section).previous
+    assert_nil leaves(:reading_picture).next
+  end
+
+  test "only active items are included as neighbours" do
+    assert_equal leaves(:summary_page), leaves(:welcome_page).next
+
+    leaves(:summary_page).trashed!
+
+    assert_equal leaves(:reading_picture), leaves(:welcome_page).next
+  end
+
+  test "only active items are counted when determining position" do
+    leaves(:welcome_page).trashed!
+
+    leaves(:welcome_section).move_to_position(1)
+    assert_equal [ leaves(:summary_page), leaves(:welcome_section), leaves(:reading_picture) ], @leaves.reload.active
+
+    leaves(:welcome_section).move_to_position(0)
+    assert_equal [ leaves(:welcome_section), leaves(:summary_page), leaves(:reading_picture) ], @leaves.reload.active
+  end
+end