From 7cc064b4a88d07046913337e235b94c93991197b Mon Sep 17 00:00:00 2001
From: Sean Dickinson <sean@bythepixel.com>
Date: Sat, 31 Oct 2026 16:36:20 -0400
Subject: [PATCH 1/2] feat: give contents ownership of module membership and
 order

Links and games join modules only through contents, which append to the end of their siblings.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
---
 .../admin/content_modules_controller.rb       |  2 +-
 app/controllers/admin/games_controller.rb     |  6 +-
 app/controllers/admin/links_controller.rb     | 12 +--
 app/models/concerns/contentable.rb            |  6 +-
 app/models/concerns/ordered.rb                | 16 ++++
 app/models/content.rb                         | 13 +++-
 app/models/content_module.rb                  | 26 ++++---
 app/models/game.rb                            |  9 +--
 app/models/link.rb                            |  7 +-
 .../admin/content_modules/_form.html.erb      |  3 -
 app/views/admin/content_modules/edit.html.erb |  1 -
 app/views/admin/games/_form.html.erb          |  1 -
 app/views/admin/games/_game.html.erb          |  4 -
 app/views/admin/games/new.html.erb            |  3 -
 app/views/admin/links/_form.html.erb          |  5 +-
 app/views/admin/links/edit.html.erb           |  2 +-
 app/views/admin/links/new.html.erb            |  2 +-
 ...20261031181034_add_position_to_contents.rb | 19 +++++
 ...ove_content_module_from_links_and_games.rb | 27 +++++++
 db/schema.rb                                  | 12 +--
 db/seeds.rb                                   | 33 +++++++-
 .../admin/content_modules_controller_test.rb  | 21 +++--
 .../admin/games_controller_test.rb            | 11 +--
 .../admin/links_controller_test.rb            |  9 ++-
 test/fixtures/contents.yml                    |  8 +-
 test/fixtures/games.yml                       |  2 -
 test/fixtures/links.yml                       |  2 -
 test/models/content_module_test.rb            | 77 +++++++++++++++++--
 test/models/content_test.rb                   | 45 +++++++++++
 test/models/game_test.rb                      | 31 ++++++--
 test/models/link_test.rb                      | 21 ++++-
 31 files changed, 334 insertions(+), 102 deletions(-)
 create mode 100644 db/migrate/20261031181034_add_position_to_contents.rb
 create mode 100644 db/migrate/20261031181544_remove_content_module_from_links_and_games.rb

diff --git a/app/controllers/admin/content_modules_controller.rb b/app/controllers/admin/content_modules_controller.rb
index 1074f86..c78c544 100644
--- a/app/controllers/admin/content_modules_controller.rb
+++ b/app/controllers/admin/content_modules_controller.rb
@@ -49,6 +49,6 @@ def set_content_module
     end
 
     def content_module_params
-      params.expect(content_module: [ :name, :program_id, :level, :position ])
+      params.expect(content_module: [ :name, :program_id, :level ])
     end
 end
diff --git a/app/controllers/admin/games_controller.rb b/app/controllers/admin/games_controller.rb
index 790a6c0..3e40cb6 100644
--- a/app/controllers/admin/games_controller.rb
+++ b/app/controllers/admin/games_controller.rb
@@ -6,8 +6,7 @@ def index
   end
 
   def new
-    @game = Game.new(content_module_id: params[:content_module_id])
-    @content_module = @game.content_module
+    @game = Game.new
   end
 
   def edit
@@ -18,7 +17,6 @@ def create
 
     respond_to do |format|
       if @game.save
-        Content.create!(content_module: @game.content_module, contentable: @game) if @game.content_module
         format.html { redirect_back(fallback_location: admin_games_path, notice: "Game was successfully created.") }
       else
         format.html { render :new, status: :unprocessable_content }
@@ -53,6 +51,6 @@ def set_game
     end
 
     def game_params
-      params.expect(game: [ :title, :slug, :content_module_id, :description ])
+      params.expect(game: [ :title, :slug, :description ])
     end
 end
diff --git a/app/controllers/admin/links_controller.rb b/app/controllers/admin/links_controller.rb
index 219330f..be7aa74 100644
--- a/app/controllers/admin/links_controller.rb
+++ b/app/controllers/admin/links_controller.rb
@@ -3,14 +3,15 @@ class Admin::LinksController < AdminController
   before_action :set_link, only: %i[edit update destroy]
 
   def new
-    @link = Link.new(content_module: @content_module)
+    @link = Link.new
   end
 
   def create
-    @link = Link.new(link_params.merge(content_module: @content_module))
+    @link = Link.new(link_params)
+
+    @link.build_content(content_module: @content_module)
 
     if @link.save
-      @content_module.contents.create!(contentable: @link)
       redirect_to edit_admin_content_module_path(@content_module), notice: "Link was successfully created."
     else
       render :new, status: :unprocessable_entity
@@ -29,8 +30,9 @@ def update
   end
 
   def destroy
+    content_module = @link.content_module
     @link.destroy!
-    redirect_to edit_admin_content_module_path(@link.content_module), notice: "Link was successfully deleted.", status: :see_other
+    redirect_to edit_admin_content_module_path(content_module), notice: "Link was successfully deleted.", status: :see_other
   end
 
   private
@@ -43,6 +45,6 @@ def set_link
     end
 
     def link_params
-      params.expect(link: [ :title, :url, :link_type, :position ])
+      params.expect(link: [ :title, :url, :link_type ])
     end
 end
diff --git a/app/models/concerns/contentable.rb b/app/models/concerns/contentable.rb
index 9ce103c..6c772a4 100644
--- a/app/models/concerns/contentable.rb
+++ b/app/models/concerns/contentable.rb
@@ -1,7 +1,9 @@
+# A content owns its link, which is deleted together with it.
+# A game is shared across modules, so it is kept when a content is removed.
 module Contentable
   extend ActiveSupport::Concern
 
-  included do
-    has_one :content, as: :contentable
+  def owned_by_content?
+    false
   end
 end
diff --git a/app/models/concerns/ordered.rb b/app/models/concerns/ordered.rb
index 2e56b03..f6ea8e9 100644
--- a/app/models/concerns/ordered.rb
+++ b/app/models/concerns/ordered.rb
@@ -1,7 +1,23 @@
+# Orders records by an integer +position+ column. New records go to the end of their siblings.
+#
+# A model that includes this must define +position_siblings+, the relation of records it is
+# ordered among (for example, the contents of one module).
 module Ordered
   extend ActiveSupport::Concern
 
   included do
     scope :ordered, -> { order(:position) }
+
+    before_create :append_to_siblings
+  end
+
+  private
+
+  def position_siblings
+    raise NotImplementedError, "#{self.class} must define #position_siblings to be ordered"
+  end
+
+  def append_to_siblings
+    self.position = (position_siblings.maximum(:position) || 0) + 1
   end
 end
diff --git a/app/models/content.rb b/app/models/content.rb
index f1dc551..d1410d7 100644
--- a/app/models/content.rb
+++ b/app/models/content.rb
@@ -1,15 +1,26 @@
 class Content < ApplicationRecord
+  include Ordered
+
   belongs_to :content_module
 
   delegated_type :contentable, types: %w[Link Game]
 
+  validates :contentable_id, uniqueness: {
+    scope: [ :content_module_id, :contentable_type ],
+    message: "is already in this module"
+  }
+
   # Ensure the associated contentable record is destroyed if allowed before destroying this content.
   # This allows us to have dependent: :destroy behavior for contentable records.
   before_destroy :destroy_owned_record
 
   private
 
+  def position_siblings
+    content_module.contents
+  end
+
   def destroy_owned_record
-    contentable.destroy if contentable.destroy_with_attachable?
+    contentable.destroy if contentable.owned_by_content?
   end
 end
diff --git a/app/models/content_module.rb b/app/models/content_module.rb
index 9013471..fac8aed 100644
--- a/app/models/content_module.rb
+++ b/app/models/content_module.rb
@@ -2,18 +2,26 @@ class ContentModule < ApplicationRecord
   include Ordered
 
   belongs_to :program
-  has_many :contents, dependent: :destroy
-  has_many :links, -> { ordered },
-    through: :contents,
-    source: :contentable,
-    source_type: "Link"
-  has_many :games,
-    through: :contents,
-    source: :contentable,
-    source_type: "Game"
+  has_many :contents, -> { ordered }, dependent: :destroy
+  has_many :games, through: :contents, source: :contentable, source_type: "Game"
+  has_many :links, through: :contents, source: :contentable, source_type: "Link"
   has_many :classroom_modules, dependent: :restrict_with_error
 
   enum :level, { basic: "basic", moderate: "moderate", advanced: "advanced" }, validate: true
 
   validates :name, :level, presence: true
+
+  # A module that joins another program or level goes to the end of it.
+  before_update :append_to_siblings, if: -> { program_id_changed? || level_changed? }
+
+  def available_games
+    Game.where.not(id: games).order(:title)
+  end
+
+  private
+
+  # Modules are ordered within one program and level, the same grouping the admin index shows.
+  def position_siblings
+    program.content_modules.where(level: level)
+  end
 end
diff --git a/app/models/game.rb b/app/models/game.rb
index 38d9fb5..7c0cad3 100644
--- a/app/models/game.rb
+++ b/app/models/game.rb
@@ -1,15 +1,10 @@
 class Game < ApplicationRecord
   include Contentable
 
-  belongs_to :content_module, optional: true
-  has_many :game_attempts, dependent: :destroy
-
+  has_many :contents, as: :contentable, dependent: :destroy
+  has_many :content_modules, through: :contents
   has_many :game_attempts, dependent: :destroy
 
   validates :title, :slug, presence: true
   validates :title, :slug, uniqueness: true
-
-  def destroy_with_attachable?
-    false
-  end
 end
diff --git a/app/models/link.rb b/app/models/link.rb
index 48ab603..f12510a 100644
--- a/app/models/link.rb
+++ b/app/models/link.rb
@@ -1,15 +1,16 @@
 class Link < ApplicationRecord
-  include Ordered
   include Contentable
 
-  belongs_to :content_module
+  # :delete skips Content callbacks to avoid a destroy loop
+  has_one :content, as: :contentable, dependent: :delete
+  has_one :content_module, through: :content
 
   enum :link_type, { survey: "survey" }, validate: true
 
   validates :title, :url, :link_type, presence: true
   validates :url, format: { with: /\Ahttps?:\/\/.+\z/i, message: "must start with http:// or https://" }, allow_blank: true
 
-  def destroy_with_attachable?
+  def owned_by_content?
     true
   end
 end
diff --git a/app/views/admin/content_modules/_form.html.erb b/app/views/admin/content_modules/_form.html.erb
index c9449b5..c343ada 100644
--- a/app/views/admin/content_modules/_form.html.erb
+++ b/app/views/admin/content_modules/_form.html.erb
@@ -22,9 +22,6 @@
     <%= form.select :level, ContentModule.levels.keys.map { |l| [ l.humanize, l ] },
           { include_blank: "Select a level" }, class: "select w-full" %>
 
-    <%= form.label :position, class: "label" %>
-    <%= form.number_field :position, class: "input w-full" %>
-
     <%= form.submit class: "btn btn-primary" %>
   </div>
 <% end %>
diff --git a/app/views/admin/content_modules/edit.html.erb b/app/views/admin/content_modules/edit.html.erb
index 0ef6e3b..ad81a80 100644
--- a/app/views/admin/content_modules/edit.html.erb
+++ b/app/views/admin/content_modules/edit.html.erb
@@ -57,7 +57,6 @@
       <div class="card-body">
         <div class="flex justify-between items-center mb-2">
           <h2 class="card-title text-lg">Games</h2>
-          <%= link_to "Add game", new_admin_game_path(content_module_id: @content_module.id), class: "btn btn-sm btn-primary" %>
         </div>
         <% if @content_module.games.any? %>
           <table class="table">
diff --git a/app/views/admin/games/_form.html.erb b/app/views/admin/games/_form.html.erb
index e16b914..a17e651 100644
--- a/app/views/admin/games/_form.html.erb
+++ b/app/views/admin/games/_form.html.erb
@@ -1,5 +1,4 @@
 <%= form_with(model: [:admin, game]) do |form| %>
-  <%= form.hidden_field :content_module_id if game.content_module_id.present? %>
   <div class="flex flex-col gap-2">
     <% if game.errors.any? %>
       <div style="color: red">
diff --git a/app/views/admin/games/_game.html.erb b/app/views/admin/games/_game.html.erb
index f7ddbd7..f585356 100644
--- a/app/views/admin/games/_game.html.erb
+++ b/app/views/admin/games/_game.html.erb
@@ -7,10 +7,6 @@
     <strong class="block font-medium mb-1">Slug:</strong>
     <%= game.slug %>
   </div>
-  <div>
-    <strong class="block font-medium mb-1">Content module:</strong>
-    <%= game.content_module_id %>
-  </div>
   <div>
     <strong class="block font-medium mb-1">Description:</strong>
     <%= game.description %>
diff --git a/app/views/admin/games/new.html.erb b/app/views/admin/games/new.html.erb
index 1cfe2e0..99983d5 100644
--- a/app/views/admin/games/new.html.erb
+++ b/app/views/admin/games/new.html.erb
@@ -3,9 +3,6 @@
 <nav class="breadcrumbs text-sm">
   <ul>
     <li><%= link_to "Content Modules", admin_content_modules_path %></li>
-    <% if @content_module %>
-      <li><%= link_to @content_module.name, edit_admin_content_module_path(@content_module) %></li>
-    <% end %>
     <li>New Game</li>
   </ul>
 </nav>
diff --git a/app/views/admin/links/_form.html.erb b/app/views/admin/links/_form.html.erb
index 4709ee3..a897152 100644
--- a/app/views/admin/links/_form.html.erb
+++ b/app/views/admin/links/_form.html.erb
@@ -1,4 +1,4 @@
-<%= form_with(model: link.persisted? ? [:admin, link] : [:admin, link.content_module, link]) do |form| %>
+<%= form_with(model: link.persisted? ? [:admin, link] : [:admin, content_module, link]) do |form| %>
   <div class="flex flex-col gap-2">
     <% if link.errors.any? %>
       <div style="color: red">
@@ -21,9 +21,6 @@
     <%= form.select :link_type, Link.link_types.keys.map { |t| [ t.humanize, t ] },
           { include_blank: "Select a type" }, class: "select w-full" %>
 
-    <%= form.label :position, class: "label" %>
-    <%= form.number_field :position, class: "input w-full" %>
-
     <%= form.submit class: "btn btn-primary" %>
   </div>
 <% end %>
diff --git a/app/views/admin/links/edit.html.erb b/app/views/admin/links/edit.html.erb
index b9db752..bba1e74 100644
--- a/app/views/admin/links/edit.html.erb
+++ b/app/views/admin/links/edit.html.erb
@@ -11,7 +11,7 @@
   <div class="card card-border bg-base-100 shadow-md w-96">
     <div class="card-body">
       <h1 class="card-title">Edit Link</h1>
-      <%= render "form", link: @link %>
+      <%= render "form", link: @link, content_module: @link.content_module %>
     </div>
   </div>
 </section>
diff --git a/app/views/admin/links/new.html.erb b/app/views/admin/links/new.html.erb
index 35513db..05b0d88 100644
--- a/app/views/admin/links/new.html.erb
+++ b/app/views/admin/links/new.html.erb
@@ -11,7 +11,7 @@
   <div class="card card-border bg-base-100 shadow-md w-96">
     <div class="card-body">
       <h1 class="card-title">New Link</h1>
-      <%= render "form", link: @link %>
+      <%= render "form", link: @link, content_module: @content_module %>
     </div>
   </div>
 </section>
diff --git a/db/migrate/20261031181034_add_position_to_contents.rb b/db/migrate/20261031181034_add_position_to_contents.rb
new file mode 100644
index 0000000..b751586
--- /dev/null
+++ b/db/migrate/20261031181034_add_position_to_contents.rb
@@ -0,0 +1,19 @@
+class AddPositionToContents < ActiveRecord::Migration[8.1]
+  def change
+    add_column :contents, :position, :integer
+    add_index :contents, [ :content_module_id, :position ]
+    add_index :contents, [ :content_module_id, :contentable_type, :contentable_id ], unique: true, name: "index_contents_on_module_and_contentable"
+
+    reversible do |dir|
+      dir.up do
+        # Numbers contents in id order, so link positions set before this migration are not kept.
+        execute <<~SQL
+          UPDATE contents SET position = (
+            SELECT COUNT(*) FROM contents earlier
+            WHERE earlier.content_module_id = contents.content_module_id AND earlier.id <= contents.id
+          )
+        SQL
+      end
+    end
+  end
+end
diff --git a/db/migrate/20261031181544_remove_content_module_from_links_and_games.rb b/db/migrate/20261031181544_remove_content_module_from_links_and_games.rb
new file mode 100644
index 0000000..51b9ca4
--- /dev/null
+++ b/db/migrate/20261031181544_remove_content_module_from_links_and_games.rb
@@ -0,0 +1,27 @@
+class RemoveContentModuleFromLinksAndGames < ActiveRecord::Migration[8.1]
+  def up
+    remove_reference :links, :content_module, foreign_key: true, index: true
+    remove_column :links, :position
+    remove_reference :games, :content_module, foreign_key: true, index: true
+  end
+
+  def down
+    add_reference :links, :content_module, foreign_key: true, index: true
+    add_column :links, :position, :integer
+    add_reference :games, :content_module, foreign_key: true, index: true
+
+    execute <<~SQL
+      UPDATE links SET
+        content_module_id = (SELECT content_module_id FROM contents WHERE contentable_type = 'Link' AND contentable_id = links.id),
+        position = (SELECT position FROM contents WHERE contentable_type = 'Link' AND contentable_id = links.id)
+    SQL
+
+    # A game can be in many modules, but the old column held one, so pick the lowest content id.
+    execute <<~SQL
+      UPDATE games SET
+        content_module_id = (SELECT content_module_id FROM contents WHERE contentable_type = 'Game' AND contentable_id = games.id ORDER BY id LIMIT 1)
+    SQL
+
+    change_column_null :links, :content_module_id, false
+  end
+end
diff --git a/db/schema.rb b/db/schema.rb
index a58913e..fc75edd 100644
--- a/db/schema.rb
+++ b/db/schema.rb
@@ -10,7 +10,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema[8.1].define(version: 2026_08_29_190944) do
+ActiveRecord::Schema[8.1].define(version: 2026_10_31_181544) do
   create_table "classroom_modules", force: :cascade do |t|
     t.integer "classroom_program_id", null: false
     t.integer "content_module_id", null: false
@@ -60,7 +60,10 @@
     t.integer "contentable_id", null: false
     t.string "contentable_type", null: false
     t.datetime "created_at", null: false
+    t.integer "position"
     t.datetime "updated_at", null: false
+    t.index ["content_module_id", "contentable_type", "contentable_id"], name: "index_contents_on_module_and_contentable", unique: true
+    t.index ["content_module_id", "position"], name: "index_contents_on_content_module_id_and_position"
     t.index ["content_module_id"], name: "index_contents_on_content_module_id"
     t.index ["contentable_type", "contentable_id"], name: "index_contents_on_contentable"
   end
@@ -81,25 +84,20 @@
   end
 
   create_table "games", force: :cascade do |t|
-    t.integer "content_module_id"
     t.datetime "created_at", null: false
     t.text "description"
     t.string "slug", null: false
     t.string "title", null: false
     t.datetime "updated_at", null: false
-    t.index ["content_module_id"], name: "index_games_on_content_module_id"
     t.index ["slug"], name: "index_games_on_slug", unique: true
   end
 
   create_table "links", force: :cascade do |t|
-    t.integer "content_module_id", null: false
     t.datetime "created_at", null: false
     t.string "link_type", null: false
-    t.integer "position"
     t.string "title", null: false
     t.datetime "updated_at", null: false
     t.string "url", null: false
-    t.index ["content_module_id"], name: "index_links_on_content_module_id"
   end
 
   create_table "programs", force: :cascade do |t|
@@ -172,8 +170,6 @@
   add_foreign_key "contents", "content_modules"
   add_foreign_key "game_attempts", "games"
   add_foreign_key "game_attempts", "students"
-  add_foreign_key "games", "content_modules"
-  add_foreign_key "links", "content_modules"
   add_foreign_key "sessions", "users"
   add_foreign_key "student_sessions", "students"
   add_foreign_key "students", "classrooms"
diff --git a/db/seeds.rb b/db/seeds.rb
index d8385d2..c064636 100644
--- a/db/seeds.rb
+++ b/db/seeds.rb
@@ -16,13 +16,38 @@ def maybe(&block)
 # Production should not have any seeded data for the content or schools
 return if Rails.env.production?
 
+fruit_veggie_quiz = Game.find_or_create_by!(slug: "fruit-veggie-quiz") do |game|
+  game.title = "Fruit and Veggie Quiz"
+  game.description = "Sort fruits and vegetables into the right food groups."
+end
+sleep_habits = Game.find_or_create_by!(slug: "sleep-habits") do |game|
+  game.title = "Sleep Habits"
+  game.description = "Pick the habits that help you get a good night's sleep."
+end
+# Intentionally not attached to any module so the "Add game" dropdown has an option.
+Game.find_or_create_by!(slug: "hydration-heroes") do |game|
+  game.title = "Hydration Heroes"
+  game.description = "Learn how much water your body needs each day."
+end
+games_by_program = { programs.first => fruit_veggie_quiz, programs.last => sleep_habits }
+
+# The first module of each program and level has a survey then a game.
+# The second module of the basic level has a game then a survey.
+# Other modules have only a survey.
 ContentModule.levels.keys.each do |level|
   programs.each do |program|
+    game = games_by_program.fetch(program)
     2.times do |i|
-      mod = program.content_modules.create!(name: "#{program.name} #{level.humanize} Module #{i + 1}", level: level, position: i + 1)
-      # TODO: Update this when the delegated types migration is completed
-      link = Link.new(title: "Survey #{i + 1}", url: "https://example.com/survey/#{program.id}-#{level}-#{i}", link_type: "survey", position: 1, content_module: mod)
-      mod.contents.create! contentable: link
+      mod = program.content_modules.create!(name: "#{program.name} #{level.humanize} Module #{i + 1}", level: level)
+      link = Link.new(title: "Survey #{i + 1}", url: "https://example.com/survey/#{program.id}-#{level}-#{i}", link_type: "survey")
+      contentables = if i.zero?
+        [ link, game ]
+      elsif level == "basic"
+        [ game, link ]
+      else
+        [ link ]
+      end
+      contentables.each { |contentable| mod.contents.create!(contentable: contentable) }
     end
   end
 end
diff --git a/test/controllers/admin/content_modules_controller_test.rb b/test/controllers/admin/content_modules_controller_test.rb
index 1336eb3..639c00e 100644
--- a/test/controllers/admin/content_modules_controller_test.rb
+++ b/test/controllers/admin/content_modules_controller_test.rb
@@ -25,12 +25,22 @@ class Admin::ContentModulesControllerTest < ActionDispatch::IntegrationTest
   test "should create content module" do
     assert_difference "ContentModule.count" do
       post admin_content_modules_url, params: {
-        content_module: { name: "New Module", program_id: programs(:one).id, level: "moderate", position: 1 }
+        content_module: { name: "New Module", program_id: programs(:one).id, level: "moderate" }
       }
     end
     assert_redirected_to admin_content_modules_url
   end
 
+  test "create appends the module and ignores a submitted position" do
+    ContentModule.create!(program: programs(:one), level: "moderate", name: "Existing")
+
+    post admin_content_modules_url, params: {
+      content_module: { name: "New Module", program_id: programs(:one).id, level: "moderate", position: 99 }
+    }
+
+    assert_equal 2, ContentModule.find_by!(name: "New Module").position
+  end
+
   test "should not create with missing name" do
     assert_no_difference "ContentModule.count" do
       post admin_content_modules_url, params: {
@@ -46,11 +56,10 @@ class Admin::ContentModulesControllerTest < ActionDispatch::IntegrationTest
   end
 
   test "edit lists links ordered by position" do
-    @content_module.links.destroy_all
-    last_link = Link.create!(content_module: @content_module, title: "Last Link", url: "https://example.com/2", link_type: "survey", position: 2)
-    first_link = Link.create!(content_module: @content_module, title: "First Link", url: "https://example.com/1", link_type: "survey", position: 1)
-    Content.create!(content_module: @content_module, contentable: last_link)
-    Content.create!(content_module: @content_module, contentable: first_link)
+    contents(:two).destroy!
+    @content_module.contents.create!(contentable: Link.new(title: "Last Link", url: "https://example.com/2", link_type: "survey"))
+    first = @content_module.contents.create!(contentable: Link.new(title: "First Link", url: "https://example.com/1", link_type: "survey"))
+    first.update!(position: 0)
 
     get edit_admin_content_module_url(@content_module)
 
diff --git a/test/controllers/admin/games_controller_test.rb b/test/controllers/admin/games_controller_test.rb
index 6fae0f6..d3f4b9e 100644
--- a/test/controllers/admin/games_controller_test.rb
+++ b/test/controllers/admin/games_controller_test.rb
@@ -3,7 +3,6 @@
 class Admin::GamesControllerTest < ActionDispatch::IntegrationTest
   setup do
     @game = games(:one)
-    @content_module = content_modules(:one)
     sign_in_as users(:one)
   end
 
@@ -13,13 +12,15 @@ class Admin::GamesControllerTest < ActionDispatch::IntegrationTest
   end
 
   test "should get new" do
-    get new_admin_game_url(content_module_id: @content_module.id)
+    get new_admin_game_url
     assert_response :success
   end
 
-  test "should create game" do
-    assert_difference [ "Game.count", "Content.count" ] do
-      post admin_games_url, params: { game: { slug: "new-game", title: "New Game", content_module_id: @content_module.id } }
+  test "creating a game does not add it to a module" do
+    assert_difference "Game.count" do
+      assert_no_difference "Content.count" do
+        post admin_games_url, params: { game: { slug: "new-game", title: "New Game" } }
+      end
     end
 
     assert_redirected_to admin_games_url
diff --git a/test/controllers/admin/links_controller_test.rb b/test/controllers/admin/links_controller_test.rb
index 8e9a7a5..72ed1b4 100644
--- a/test/controllers/admin/links_controller_test.rb
+++ b/test/controllers/admin/links_controller_test.rb
@@ -12,17 +12,18 @@ class Admin::LinksControllerTest < ActionDispatch::IntegrationTest
     assert_response :success
   end
 
-  test "should create link" do
-    assert_difference "Link.count" do
+  test "create adds the new link to the end of the module" do
+    assert_difference [ "Link.count", "@mod.contents.count" ], 1 do
       post admin_content_module_links_url(@mod), params: {
-        link: { title: "New Survey", url: "https://example.com/new", link_type: "survey", position: 3 }
+        link: { title: "New Survey", url: "https://example.com/new", link_type: "survey" }
       }
     end
     assert_redirected_to edit_admin_content_module_url(@mod)
+    assert_equal "New Survey", @mod.contents.last.contentable.title
   end
 
   test "should not create with missing title" do
-    assert_no_difference "Link.count" do
+    assert_no_difference [ "Link.count", "Content.count" ] do
       post admin_content_module_links_url(@mod), params: {
         link: { title: "", url: "https://example.com", link_type: "survey" }
       }
diff --git a/test/fixtures/contents.yml b/test/fixtures/contents.yml
index 1d64a6d..d60d7f6 100644
--- a/test/fixtures/contents.yml
+++ b/test/fixtures/contents.yml
@@ -2,10 +2,10 @@
 
 one:
   content_module: one
-  contentable_id: <%= ActiveRecord::FixtureSet.identify(:one) %>
-  contentable_type: Game
+  contentable: one (Game)
+  position: 1
 
 two:
   content_module: one
-  contentable_id: <%= ActiveRecord::FixtureSet.identify(:one) %>
-  contentable_type: Link
+  contentable: one (Link)
+  position: 2
diff --git a/test/fixtures/games.yml b/test/fixtures/games.yml
index bd0ba0c..14779e4 100644
--- a/test/fixtures/games.yml
+++ b/test/fixtures/games.yml
@@ -3,11 +3,9 @@
 one:
   title: Game 1
   slug: game-1
-  content_module: one
   description: MyText
 
 two:
   title: Game 2
   slug: game-2
-  content_module: one
   description: MyText
diff --git a/test/fixtures/links.yml b/test/fixtures/links.yml
index c6fce72..e6b2526 100644
--- a/test/fixtures/links.yml
+++ b/test/fixtures/links.yml
@@ -1,6 +1,4 @@
 one:
-  content_module: one
   title: Health Survey
   url: https://example.com/survey/1
   link_type: survey
-  position: 1
diff --git a/test/models/content_module_test.rb b/test/models/content_module_test.rb
index c8df5bd..3a1c3d9 100644
--- a/test/models/content_module_test.rb
+++ b/test/models/content_module_test.rb
@@ -28,17 +28,77 @@ class ContentModuleTest < ActiveSupport::TestCase
 
   test "destroys associated links" do
     content_module = ContentModule.create!(program: @program, level: "basic", name: "With Links")
-    link = Link.create!(content_module: content_module, title: "A Link", url: "https://example.com", link_type: "survey")
-    Content.create!(content_module: content_module, contentable: link)
+    link = Link.new(title: "A Link", url: "https://example.com", link_type: "survey")
+    content_module.contents.create!(contentable: link)
 
     assert_difference "Link.count", -1 do
       content_module.destroy!
     end
   end
 
-  test "exposes delegated contentables" do
-    assert_equal [ links(:one) ], content_modules(:one).links.to_a
-    assert_equal [ games(:one) ], content_modules(:one).games.to_a
+  test "available games exclude games already in the module" do
+    assert_not_includes content_modules(:one).available_games, games(:one)
+  end
+
+  test "available games include games only in another module" do
+    other_module = ContentModule.create!(program: @program, level: "basic", name: "Other Module")
+    other_module.contents.create!(contentable: games(:two))
+
+    assert_includes content_modules(:one).available_games, games(:two)
+  end
+
+  test "available games include unattached games" do
+    assert_includes content_modules(:one).available_games, games(:two)
+  end
+
+  test "returns contents ordered by position" do
+    contents(:one).update!(position: 2)
+    contents(:two).update!(position: 1)
+
+    assert_equal [ contents(:two), contents(:one) ], content_modules(:one).contents.to_a
+  end
+
+  test "appends new modules after the highest position in their program and level" do
+    first = create_module("First")
+    second = create_module("Second")
+
+    assert_equal [ 1, 2 ], [ first.position, second.position ]
+  end
+
+  test "positions are separate for each level and program" do
+    create_module("Advanced")
+    moderate = create_module("Moderate", level: "moderate")
+    other_program = create_module("Other", program: programs(:two))
+
+    assert_equal 1, moderate.position
+    assert_equal 1, other_program.position
+  end
+
+  test "moves to the end of its new level when the level changes" do
+    mod = create_module("Advanced")
+    create_module("Moderate", level: "moderate")
+
+    mod.update!(level: "moderate")
+
+    assert_equal 2, mod.position
+  end
+
+  test "moves to the end of its new program when the program changes" do
+    mod = create_module("Advanced")
+    create_module("Other", program: programs(:two))
+
+    mod.update!(program: programs(:two))
+
+    assert_equal 2, mod.position
+  end
+
+  test "keeps its position when other fields change" do
+    first = create_module("First")
+    create_module("Second")
+
+    first.update!(name: "Renamed")
+
+    assert_equal 1, first.reload.position
   end
 
   test "cannot be destroyed when classroom modules exist" do
@@ -49,4 +109,11 @@ class ContentModuleTest < ActiveSupport::TestCase
     assert_not content_module.destroy
     assert content_module.persisted?
   end
+
+  private
+
+  # Defaults to a level no fixture uses, so positions start empty.
+  def create_module(name, program: @program, level: "advanced", **attributes)
+    ContentModule.create!(program: program, level: level, name: name, **attributes)
+  end
 end
diff --git a/test/models/content_test.rb b/test/models/content_test.rb
index e006b41..281814b 100644
--- a/test/models/content_test.rb
+++ b/test/models/content_test.rb
@@ -13,4 +13,49 @@ class ContentTest < ActiveSupport::TestCase
 
     assert_equal content_modules(:one), content.content_module
   end
+
+  test "appends new content after the highest position in its module" do
+    content = content_modules(:one).contents.create!(contentable: games(:two))
+
+    assert_equal 3, content.position
+  end
+
+  test "starts positions at 1 in an empty module" do
+    content = create_module.contents.create!(contentable: games(:one))
+
+    assert_equal 1, content.position
+  end
+
+  test "cannot add the same game to a module twice" do
+    duplicate = content_modules(:one).contents.build(contentable: games(:one))
+
+    assert_not duplicate.valid?
+    assert_includes duplicate.errors[:contentable_id], "is already in this module"
+  end
+
+  test "can add the same game to different modules" do
+    content = create_module.contents.build(contentable: games(:one))
+
+    assert content.valid?
+  end
+
+  test "destroying a link's content destroys the link" do
+    assert_difference [ "Link.count", "Content.count" ], -1 do
+      contents(:two).destroy!
+    end
+  end
+
+  test "destroying a game's content keeps the game" do
+    assert_difference "Content.count", -1 do
+      assert_no_difference "Game.count" do
+        contents(:one).destroy!
+      end
+    end
+  end
+
+  private
+
+  def create_module
+    ContentModule.create!(program: programs(:one), level: "basic", name: "Another Module")
+  end
 end
diff --git a/test/models/game_test.rb b/test/models/game_test.rb
index 3622a6f..cd070bf 100644
--- a/test/models/game_test.rb
+++ b/test/models/game_test.rb
@@ -2,26 +2,41 @@
 
 class GameTest < ActiveSupport::TestCase
   test "should not save game without title" do
-    game = Game.new(slug: "test-slug", content_module: ContentModule.new)
+    game = Game.new(slug: "test-slug")
     assert_not game.save, "Saved the game without a title"
   end
 
   test "should not save game without slug" do
-    game = Game.new(title: "Test Game", content_module: ContentModule.new)
+    game = Game.new(title: "Test Game")
     assert_not game.save, "Saved the game without a slug"
   end
 
   test "should not save game with duplicate title" do
-    content_module = ContentModule.create!(program: programs(:one), level: "basic", name: "Test Module")
-    Game.create!(title: "Test Game", slug: "test-slug", content_module: content_module)
-    duplicate_game = Game.new(title: "Test Game", slug: "another-slug", content_module: content_module)
+    Game.create!(title: "Test Game", slug: "test-slug")
+    duplicate_game = Game.new(title: "Test Game", slug: "another-slug")
     assert_not duplicate_game.save, "Saved the game with a duplicate title"
   end
 
+  test "destroying a game destroys all its contents" do
+    other_module = ContentModule.create!(program: programs(:one), level: "basic", name: "Other Module")
+    other_module.contents.create!(contentable: games(:one))
+
+    assert_difference "Content.count", -2 do
+      games(:one).destroy!
+    end
+    assert_empty Content.where(contentable: games(:one))
+  end
+
+  test "destroying a game deletes its student attempts" do
+    assert_difference "GameAttempt.count", -games(:one).game_attempts.count do
+      games(:one).destroy!
+    end
+    assert_empty GameAttempt.where(game: games(:one))
+  end
+
   test "should not save game with duplicate slug" do
-    content_module = ContentModule.create!(program: programs(:one), level: "basic", name: "Test Module")
-    Game.create!(title: "Test Game", slug: "test-slug", content_module: content_module)
-    duplicate_game = Game.new(title: "Another Game", slug: "test-slug", content_module: content_module)
+    Game.create!(title: "Test Game", slug: "test-slug")
+    duplicate_game = Game.new(title: "Another Game", slug: "test-slug")
     assert_not duplicate_game.save, "Saved the game with a duplicate slug"
   end
 end
diff --git a/test/models/link_test.rb b/test/models/link_test.rb
index c1889be..f357244 100644
--- a/test/models/link_test.rb
+++ b/test/models/link_test.rb
@@ -2,24 +2,37 @@
 
 class LinkTest < ActiveSupport::TestCase
   test "is valid with required fields" do
-    link = Link.new(content_module: content_modules(:one), title: "My Link", url: "https://example.com", link_type: "survey")
+    link = Link.new(title: "My Link", url: "https://example.com", link_type: "survey")
     assert link.valid?
   end
 
   test "is invalid without a title" do
-    link = Link.new(content_module: content_modules(:one), url: "https://example.com", link_type: "survey")
+    link = Link.new(url: "https://example.com", link_type: "survey")
     assert_not link.valid?
     assert_includes link.errors[:title], "can't be blank"
   end
 
   test "is invalid without a url" do
-    link = Link.new(content_module: content_modules(:one), title: "My Link", link_type: "survey")
+    link = Link.new(title: "My Link", link_type: "survey")
     assert_not link.valid?
     assert_includes link.errors[:url], "can't be blank"
   end
 
+  test "destroying a link destroys its content" do
+    content_id = contents(:two).id
+
+    assert_difference [ "Link.count", "Content.count" ], -1 do
+      links(:one).destroy!
+    end
+    assert_nil Content.find_by(id: content_id)
+  end
+
+  test "finds its content module through its content" do
+    assert_equal content_modules(:one), links(:one).content_module
+  end
+
   test "is invalid without a link_type" do
-    link = Link.new(content_module: content_modules(:one), title: "My Link", url: "https://example.com")
+    link = Link.new(title: "My Link", url: "https://example.com")
     assert_not link.valid?
   end
 end

From f1c06db7dd511f059813d7f380d28f05fa07dd1b Mon Sep 17 00:00:00 2001
From: Sean Dickinson <sean@bythepixel.com>
Date: Sat, 31 Oct 2026 19:54:38 -0400
Subject: [PATCH 2/2] fix: updates

---
 app/models/concerns/contentable.rb            |  5 ++-
 app/models/concerns/ordered.rb                |  7 ++--
 app/models/content_module.rb                  |  5 +--
 app/models/game.rb                            |  2 +
 ...20261031181034_add_position_to_contents.rb | 12 ------
 ...ove_content_module_from_links_and_games.rb | 18 +--------
 db/seeds.rb                                   |  1 +
 skills/rails-test-fixtures-conventions.md     | 28 +++++++++++---
 .../admin/content_modules_controller_test.rb  | 13 ++++---
 test/models/content_module_test.rb            | 26 ++++---------
 test/models/content_test.rb                   | 38 ++++++++++++++-----
 test/models/game_test.rb                      | 28 ++++++++++++--
 test/models/link_test.rb                      | 12 ++++--
 13 files changed, 109 insertions(+), 86 deletions(-)

diff --git a/app/models/concerns/contentable.rb b/app/models/concerns/contentable.rb
index 6c772a4..51acc30 100644
--- a/app/models/concerns/contentable.rb
+++ b/app/models/concerns/contentable.rb
@@ -1,8 +1,9 @@
-# A content owns its link, which is deleted together with it.
-# A game is shared across modules, so it is kept when a content is removed.
 module Contentable
   extend ActiveSupport::Concern
 
+  # Whether the content record owns this contentable, so the contentable is destroyed together with it.
+  #
+  # @return [Boolean]
   def owned_by_content?
     false
   end
diff --git a/app/models/concerns/ordered.rb b/app/models/concerns/ordered.rb
index f6ea8e9..c846074 100644
--- a/app/models/concerns/ordered.rb
+++ b/app/models/concerns/ordered.rb
@@ -1,7 +1,4 @@
 # Orders records by an integer +position+ column. New records go to the end of their siblings.
-#
-# A model that includes this must define +position_siblings+, the relation of records it is
-# ordered among (for example, the contents of one module).
 module Ordered
   extend ActiveSupport::Concern
 
@@ -13,6 +10,10 @@ module Ordered
 
   private
 
+  # This method is required to override. It is the relation of records this record is
+  # ordered among (for example, the contents of one module).
+  #
+  # @return [ActiveRecord::Relation]
   def position_siblings
     raise NotImplementedError, "#{self.class} must define #position_siblings to be ordered"
   end
diff --git a/app/models/content_module.rb b/app/models/content_module.rb
index fac8aed..3ea5e0f 100644
--- a/app/models/content_module.rb
+++ b/app/models/content_module.rb
@@ -12,12 +12,9 @@ class ContentModule < ApplicationRecord
   validates :name, :level, presence: true
 
   # A module that joins another program or level goes to the end of it.
+  # TODO: Consider if we just don't allow these types of edits to avoid this hidden callback behavior
   before_update :append_to_siblings, if: -> { program_id_changed? || level_changed? }
 
-  def available_games
-    Game.where.not(id: games).order(:title)
-  end
-
   private
 
   # Modules are ordered within one program and level, the same grouping the admin index shows.
diff --git a/app/models/game.rb b/app/models/game.rb
index 7c0cad3..b3f096b 100644
--- a/app/models/game.rb
+++ b/app/models/game.rb
@@ -7,4 +7,6 @@ class Game < ApplicationRecord
 
   validates :title, :slug, presence: true
   validates :title, :slug, uniqueness: true
+
+  scope :available_for, ->(content_module) { where.not(id: content_module.games).order(:title) }
 end
diff --git a/db/migrate/20261031181034_add_position_to_contents.rb b/db/migrate/20261031181034_add_position_to_contents.rb
index b751586..71e34ab 100644
--- a/db/migrate/20261031181034_add_position_to_contents.rb
+++ b/db/migrate/20261031181034_add_position_to_contents.rb
@@ -3,17 +3,5 @@ def change
     add_column :contents, :position, :integer
     add_index :contents, [ :content_module_id, :position ]
     add_index :contents, [ :content_module_id, :contentable_type, :contentable_id ], unique: true, name: "index_contents_on_module_and_contentable"
-
-    reversible do |dir|
-      dir.up do
-        # Numbers contents in id order, so link positions set before this migration are not kept.
-        execute <<~SQL
-          UPDATE contents SET position = (
-            SELECT COUNT(*) FROM contents earlier
-            WHERE earlier.content_module_id = contents.content_module_id AND earlier.id <= contents.id
-          )
-        SQL
-      end
-    end
   end
 end
diff --git a/db/migrate/20261031181544_remove_content_module_from_links_and_games.rb b/db/migrate/20261031181544_remove_content_module_from_links_and_games.rb
index 51b9ca4..95ae340 100644
--- a/db/migrate/20261031181544_remove_content_module_from_links_and_games.rb
+++ b/db/migrate/20261031181544_remove_content_module_from_links_and_games.rb
@@ -6,22 +6,6 @@ def up
   end
 
   def down
-    add_reference :links, :content_module, foreign_key: true, index: true
-    add_column :links, :position, :integer
-    add_reference :games, :content_module, foreign_key: true, index: true
-
-    execute <<~SQL
-      UPDATE links SET
-        content_module_id = (SELECT content_module_id FROM contents WHERE contentable_type = 'Link' AND contentable_id = links.id),
-        position = (SELECT position FROM contents WHERE contentable_type = 'Link' AND contentable_id = links.id)
-    SQL
-
-    # A game can be in many modules, but the old column held one, so pick the lowest content id.
-    execute <<~SQL
-      UPDATE games SET
-        content_module_id = (SELECT content_module_id FROM contents WHERE contentable_type = 'Game' AND contentable_id = games.id ORDER BY id LIMIT 1)
-    SQL
-
-    change_column_null :links, :content_module_id, false
+    raise ActiveRecord::IrreversibleMigration
   end
 end
diff --git a/db/seeds.rb b/db/seeds.rb
index c064636..1c9ac2f 100644
--- a/db/seeds.rb
+++ b/db/seeds.rb
@@ -34,6 +34,7 @@ def maybe(&block)
 # The first module of each program and level has a survey then a game.
 # The second module of the basic level has a game then a survey.
 # Other modules have only a survey.
+# TODO: This is getting complex, we should extract this into a partial and make it more readable
 ContentModule.levels.keys.each do |level|
   programs.each do |program|
     game = games_by_program.fetch(program)
diff --git a/skills/rails-test-fixtures-conventions.md b/skills/rails-test-fixtures-conventions.md
index e2d874f..eaed12d 100644
--- a/skills/rails-test-fixtures-conventions.md
+++ b/skills/rails-test-fixtures-conventions.md
@@ -4,21 +4,39 @@ Goal: keep fixtures few. Too many fixtures = nobody understands the dependency g
 
 ## Rules
 
-1. **1-2 fixtures per model max**
+1. 1-2 fixtures per model max
     - Name them `:one` and `:two`
     - Plain, valid, boring attributes
     - Minimal dependencies
     - Add `:two` only to compare two records
 
-2. **Customize in the test, not the fixture**
+2. Customize in the test, not the fixture
     - `developers(:one).update!(field: value)`
     - Only set the field the test cares about
     - Extra DB write is fine, readability wins
 
-3. **Use a custom helper method for when needed**
+3. Use a custom helper method for when needed
     - Create a method like `create_thing` that allows customizing attributes
 
-4. **New named fixture = last resort**
+4. New named fixture = last resort
     - Only for deep/complex required associations
     - Give it a real name, not `:three` (e.g. `:paying_customer`)
-    - Max 1-2 per model
\ No newline at end of file
+    - Max 1-2 per model
+
+5. Don't use a fixture when creating data inline would be more explicit
+    - A reader should not need to reference multiple fixtures to understand implicit relationships in the test
+    - Examples
+      - Bad: The reader doesn't know that games(:one) is already in modules(:one) 
+      ```ruby
+        test "you cannot add a game more than once to the same module" do
+          refute modules(:one).contents.build(contentable: games(:one)).valid?
+        end
+      ```
+      - Good: The build the module explicitly rather than using the fixture
+      ```ruby
+        test "you cannot add a game more than once to the same module" do
+          module_with_game = create_module
+          module_with_game.contents.create!(contentable: games(:one))
+          refute module_with_game.contents.build(contentable: games(:one)).valid?
+        end
+      ```
\ No newline at end of file
diff --git a/test/controllers/admin/content_modules_controller_test.rb b/test/controllers/admin/content_modules_controller_test.rb
index 639c00e..62e74e5 100644
--- a/test/controllers/admin/content_modules_controller_test.rb
+++ b/test/controllers/admin/content_modules_controller_test.rb
@@ -56,15 +56,16 @@ class Admin::ContentModulesControllerTest < ActionDispatch::IntegrationTest
   end
 
   test "edit lists links ordered by position" do
-    contents(:two).destroy!
-    @content_module.contents.create!(contentable: Link.new(title: "Last Link", url: "https://example.com/2", link_type: "survey"))
-    first = @content_module.contents.create!(contentable: Link.new(title: "First Link", url: "https://example.com/1", link_type: "survey"))
-    first.update!(position: 0)
+    content_module = ContentModule.create!(program: programs(:one), level: "basic", name: "Ordered Module")
+    last, first = [
+      content_module.contents.create!(contentable: Link.new(title: "Last Link", url: "https://example.com/2", link_type: "survey",), position: 2),
+      content_module.contents.create!(contentable: Link.new(title: "First Link", url: "https://example.com/1", link_type: "survey"),  position: 1)
+    ]
 
-    get edit_admin_content_module_url(@content_module)
+    get edit_admin_content_module_url(content_module)
 
     hrefs = css_select("table tbody tr td:first-child a").map { |link| link["href"] }
-    assert_equal [ "https://example.com/1", "https://example.com/2" ], hrefs
+    assert_equal [ last.contentable.url, first.contentable.url ], hrefs
   end
 
   test "should update content module" do
diff --git a/test/models/content_module_test.rb b/test/models/content_module_test.rb
index 3a1c3d9..04ebd7d 100644
--- a/test/models/content_module_test.rb
+++ b/test/models/content_module_test.rb
@@ -36,26 +36,13 @@ class ContentModuleTest < ActiveSupport::TestCase
     end
   end
 
-  test "available games exclude games already in the module" do
-    assert_not_includes content_modules(:one).available_games, games(:one)
-  end
-
-  test "available games include games only in another module" do
-    other_module = ContentModule.create!(program: @program, level: "basic", name: "Other Module")
-    other_module.contents.create!(contentable: games(:two))
-
-    assert_includes content_modules(:one).available_games, games(:two)
-  end
-
-  test "available games include unattached games" do
-    assert_includes content_modules(:one).available_games, games(:two)
-  end
-
   test "returns contents ordered by position" do
-    contents(:one).update!(position: 2)
-    contents(:two).update!(position: 1)
-
-    assert_equal [ contents(:two), contents(:one) ], content_modules(:one).contents.to_a
+    content_module = create_module("With Contents")
+    first, second = [
+      content_module.contents.create!(contentable: games(:one), position: 1),
+      content_module.contents.create!(contentable: games(:two), position: 2)
+    ]
+    assert_equal [ second, first ], content_module.contents.to_a
   end
 
   test "appends new modules after the highest position in their program and level" do
@@ -113,6 +100,7 @@ class ContentModuleTest < ActiveSupport::TestCase
   private
 
   # Defaults to a level no fixture uses, so positions start empty.
+  # TODO: This can drift based on the fixture file and cause unexpected behavior. We should consider a better way to handle this.
   def create_module(name, program: @program, level: "advanced", **attributes)
     ContentModule.create!(program: program, level: level, name: name, **attributes)
   end
diff --git a/test/models/content_test.rb b/test/models/content_test.rb
index 281814b..795c55e 100644
--- a/test/models/content_test.rb
+++ b/test/models/content_test.rb
@@ -2,22 +2,27 @@
 
 class ContentTest < ActiveSupport::TestCase
   test "delegates to its contentable" do
-    content = contents(:one)
+    game = games(:one)
+    content = create_module.contents.create!(contentable: game)
 
-    assert_equal games(:one), content.contentable
+    assert_equal game, content.contentable
     assert_equal "Game", content.contentable_type
   end
 
   test "belongs to a content module" do
-    content = contents(:one)
+    content_module = create_module
+    content = content_module.contents.create!(contentable: games(:one))
 
-    assert_equal content_modules(:one), content.content_module
+    assert_equal content_module, content.content_module
   end
 
   test "appends new content after the highest position in its module" do
-    content = content_modules(:one).contents.create!(contentable: games(:two))
+    content_module = create_module
+    existing = content_module.contents.create!(contentable: games(:one))
 
-    assert_equal 3, content.position
+    content = content_module.contents.create!(contentable: games(:two))
+
+    assert_equal existing.position + 1, content.position
   end
 
   test "starts positions at 1 in an empty module" do
@@ -27,28 +32,37 @@ class ContentTest < ActiveSupport::TestCase
   end
 
   test "cannot add the same game to a module twice" do
-    duplicate = content_modules(:one).contents.build(contentable: games(:one))
+    content_module = create_module
+    content_module.contents.create!(contentable: games(:one))
+
+    duplicate = content_module.contents.build(contentable: games(:one))
 
     assert_not duplicate.valid?
     assert_includes duplicate.errors[:contentable_id], "is already in this module"
   end
 
   test "can add the same game to different modules" do
+    create_module.contents.create!(contentable: games(:one))
+
     content = create_module.contents.build(contentable: games(:one))
 
     assert content.valid?
   end
 
   test "destroying a link's content destroys the link" do
+    content = create_module.contents.create!(contentable: build_link)
+
     assert_difference [ "Link.count", "Content.count" ], -1 do
-      contents(:two).destroy!
+      content.destroy!
     end
   end
 
   test "destroying a game's content keeps the game" do
+    content = create_module.contents.create!(contentable: games(:one))
+
     assert_difference "Content.count", -1 do
       assert_no_difference "Game.count" do
-        contents(:one).destroy!
+        content.destroy!
       end
     end
   end
@@ -56,6 +70,10 @@ class ContentTest < ActiveSupport::TestCase
   private
 
   def create_module
-    ContentModule.create!(program: programs(:one), level: "basic", name: "Another Module")
+    ContentModule.create!(program: programs(:one), level: "basic", name: "Module #{ContentModule.count}")
+  end
+
+  def build_link
+    Link.new(title: "A Link", url: "https://example.com", link_type: "survey")
   end
 end
diff --git a/test/models/game_test.rb b/test/models/game_test.rb
index cd070bf..3fd2fad 100644
--- a/test/models/game_test.rb
+++ b/test/models/game_test.rb
@@ -18,13 +18,33 @@ class GameTest < ActiveSupport::TestCase
   end
 
   test "destroying a game destroys all its contents" do
-    other_module = ContentModule.create!(program: programs(:one), level: "basic", name: "Other Module")
-    other_module.contents.create!(contentable: games(:one))
+    game = Game.create!(title: "Shared Game", slug: "shared-game")
+    2.times do |i|
+      ContentModule.create!(program: programs(:one), level: "basic", name: "Module #{i}").contents.create!(contentable: game)
+    end
 
     assert_difference "Content.count", -2 do
-      games(:one).destroy!
+      game.destroy!
     end
-    assert_empty Content.where(contentable: games(:one))
+    assert_empty Content.where(contentable: game)
+  end
+
+  test "available_for returns games not in the module, ordered by title" do
+    content_module = ContentModule.create!(program: programs(:one), level: "basic", name: "Module")
+    other_module = ContentModule.create!(program: programs(:one), level: "basic", name: "Other Module")
+    in_module = Game.create!(title: "In Module", slug: "in-module").tap do
+      content_module.contents.create!(contentable: it)
+    end
+    in_other_module = Game.create!(title: "B In Other Module", slug: "in-other-module").tap do
+      other_module.contents.create!(contentable: it)
+    end
+    in_no_module = Game.create!(title: "A In No Module", slug: "in-no-module")
+
+
+    available = Game.available_for(content_module)
+
+    assert_not_includes available, in_module
+    assert_equal [ in_no_module, in_other_module ], available.where(id: [ in_module, in_other_module, in_no_module ]).to_a
   end
 
   test "destroying a game deletes its student attempts" do
diff --git a/test/models/link_test.rb b/test/models/link_test.rb
index f357244..3a4995e 100644
--- a/test/models/link_test.rb
+++ b/test/models/link_test.rb
@@ -19,16 +19,20 @@ class LinkTest < ActiveSupport::TestCase
   end
 
   test "destroying a link destroys its content" do
-    content_id = contents(:two).id
+    link = Link.new(title: "My Link", url: "https://example.com", link_type: "survey")
+    content = content_modules(:one).contents.create!(contentable: link)
 
     assert_difference [ "Link.count", "Content.count" ], -1 do
-      links(:one).destroy!
+      link.destroy!
     end
-    assert_nil Content.find_by(id: content_id)
+    assert_nil Content.find_by(id: content.id)
   end
 
   test "finds its content module through its content" do
-    assert_equal content_modules(:one), links(:one).content_module
+    link = Link.new(title: "My Link", url: "https://example.com", link_type: "survey")
+    content_modules(:one).contents.create!(contentable: link)
+
+    assert_equal content_modules(:one), link.content_module
   end
 
   test "is invalid without a link_type" do