Test UUID default value in Rails

uuid_default_test.rb

unless File.exist?("Gemfile")
  File.write("Gemfile", <<-GEMFILE)
    source "https://rubygems.org"
    gem "rails", github: "rails/rails"
    gem "pg"
  GEMFILE

  system "bundle"
end

require "bundler"
Bundler.setup(:default)

require "active_record"
require "minitest/autorun"
require "logger"

ActiveRecord::Base.establish_connection(
  adapter:  "postgresql",
  host:     "localhost",
  username: "test-default",
  database: "test-default-values"
)
ActiveRecord::Base.logger = Logger.new(STDOUT)

ActiveRecord::Schema.define do
  enable_extension "uuid-ossp"

  drop_table :posts if table_exists?(:posts)

  create_table :posts do |t|
    t.string :test_string, default: "A string."
    t.uuid   :test_key,    default: "uuid_generate_v4()"
  end
end

class Post < ActiveRecord::Base
end

class BugTest < Minitest::Test
  def test_default_string_value
    post = Post.create!

    assert_equal "A string.", post.test_string
  end

  def test_default_uuid_value
    post = Post.create!

    refute_nil post.test_key
  end

  def test_default_uuid_value_after_reload
    post = Post.create!

    refute_nil post.reload.test_key
  end
end