Add working test case

Rakefile

@@ -38,6 +38,22 @@ namespace :db do
     # File.expand_path is executed directory of generated Rails app
     rakefile = File.expand_path('Rakefile', 'test/dummy/')
     command = "rake -f '%s' db:create" % rakefile
-    sh(command) unless ENV["DISABLE_CREATE"]
+    sh(command)
+  end
+
+  task :drop do
+    # File.expand_path is executed directory of generated Rails app
+    rakefile = File.expand_path('Rakefile', 'test/dummy/')
+    command = "rake -f '%s' db:drop" % rakefile
+    sh(command)
+  end
+
+  namespace :test do
+    task :prepare do
+      # File.expand_path is executed directory of generated Rails app
+      rakefile = File.expand_path('Rakefile', 'test/dummy/')
+      command = "rake -f '%s' db:test:prepare" % rakefile
+      sh(command)
+    end
   end
 end

test/concurrency_test.rb

@@ -0,0 +1,48 @@
+require 'test_helper'
+
+# Test Models:
+#
+#   Answer       - :scope => :question_id
+#   Comment      - :scope => :question_id (with an AR default scope)
+#   Invoice      - :scope => :account_id, :start_at => 1000
+#   Product      - :scope => :account_id, :start_at => lambda { |r| r.computed_start_value }
+#   Order        - :scope => :non_existent_column
+#   User         - :scope => :account_id, :column => :custom_sequential_id
+#   Address      - :scope => :account_id ('sequential_id' does not exist)
+#   Email        - :scope => [:emailable_id, :emailable_type]
+#   Subscription - no options
+#   Rating       - :scope => :comment_id, skip: { |r| r.score == 0 }
+#   Monster      - no options
+#   Zombie       - STI, inherits from Monster
+#   Werewolf     - STI, inherits from Monster
+
+#   ConcurrentBadger - scope: :concurrent_burrow_id,
+#                      NOT NULL constraint on sequential_id,
+#                      UNIQUE constraint on sequential_id within concurrent_burrow_id scope
+
+if ENV['DB'] == 'postgresql'
+  class ActsAsSequencedTest < ActiveSupport::TestCase
+    self.use_transactional_fixtures = false
+
+    def teardown
+      ConcurrentBadger.delete_all
+    end
+
+    test "creates records concurrently without data races" do
+      Thread.abort_on_exception = true
+      range = (1..50)
+
+      threads = []
+      range.each do
+        threads << Thread.new do
+          ConcurrentBadger.create!(burrow_id: 1)
+        end
+      end
+
+      threads.each(&:join)
+
+      sequential_ids = ConcurrentBadger.pluck(:sequential_id)
+      assert_equal range.to_a, sequential_ids
+    end
+  end
+end

test/dummy/app/models/concurrent_badger.rb

@@ -0,0 +1,3 @@
+class ConcurrentBadger < ActiveRecord::Base
+  acts_as_sequenced scope: :burrow_id
+end

test/dummy/config/database.yml

@@ -15,7 +15,7 @@ postgresql: &postgresql
   min_messages: ERROR
 
 defaults: &defaults
-  pool: 5
+  pool: 100
   timeout: 5000
   host: localhost
   <<: *<%= ENV['DB'] || "sqlite" %>

test/dummy/config/environments/development.rb

@@ -22,16 +22,12 @@
   # Only use best-standards-support built into browsers
   config.action_dispatch.best_standards_support = :builtin
 
-  # Raise exception on mass assignment protection for Active Record models
-  config.active_record.mass_assignment_sanitizer = :strict
-
-  # Log the query plan for queries taking more than this (works
-  # with SQLite, MySQL, and PostgreSQL)
-  config.active_record.auto_explain_threshold_in_seconds = 0.5
-
   # Do not compress assets
   config.assets.compress = false
 
   # Expands the lines which load the assets
   config.assets.debug = true
+
+  # Required for Rails >= 4.2
+  config.eager_load = true
 end

test/dummy/config/environments/test.rb

@@ -35,4 +35,7 @@
 
   # Print deprecation notices to the stderr
   config.active_support.deprecation = :stderr
+
+  # Required for Rails >= 4.2
+  config.eager_load = true
 end

test/dummy/db/migrate/20151120190645_create_concurrent_badgers.rb

@@ -0,0 +1,10 @@
+class CreateConcurrentBadgers < ActiveRecord::Migration
+  def change
+    create_table :concurrent_badgers do |t|
+      t.integer :sequential_id, null: false
+      t.integer :burrow_id
+    end
+
+    add_index :concurrent_badgers, [:sequential_id, :burrow_id], unique: true, name: 'unique_concurrent'
+  end
+end