counter_cache_test.rb

begin
  require 'bundler/inline'
rescue LoadError => e
  $stderr.puts 'Bundler version 1.10 or later is required. Please update your Bundler'
  raise e
end

gemfile(true) do
  source 'https://rubygems.org'
  # Activate the gem you are reporting the issue against.
  gem 'activerecord', '4.2.0'
  gem 'sqlite3'
end

require 'active_record'
require 'minitest/autorun'
require 'logger'

# Ensure backward compatibility with Minitest 4
Minitest::Test = MiniTest::Unit::TestCase unless defined?(Minitest::Test)

# This connection will do for database-independent bug reports.
ActiveRecord::Base.establish_connection(adapter: 'sqlite3', database: ':memory:')
ActiveRecord::Base.logger = Logger.new(STDOUT)

ActiveRecord::Schema.define do
  create_table :schools, force: true do |t|
    t.integer :students_count, default: 0
  end

  create_table :students, force: true do |t|
    t.integer :school_id
  end
end

class School < ActiveRecord::Base
  has_many :students
end

class Student < ActiveRecord::Base
  belongs_to :school, counter_cache: true
end

class BugTest < Minitest::Test
  def test_counter_cache_update
    student = Student.create!
    school = School.create!

    student.school = school
    student.save

    assert_equal 1, school.reload.students_count
  end
end