test_database.rb

require 'active_record'
require 'active_record/connection_adapters/mysql2_adapter'

# Setups the test database with the schema_migrations table that ActiveRecord
# requires for the migrations, plus a table for the Comment model used throught
# the tests.
#
class TestDatabase
  # Constructor
  #
  # @param config [Hash]
  def initialize(config)
    @config = config
    @database = config['database']
  end

  # Creates the test database, the schema_migrations and the comments tables.
  # It drops any of them if they already exist
  def setup
    setup_test_database
    drop_and_create_schema_migrations_table
  end

  # Creates the #{@database} database and the comments table in it.
  # Before, it drops both if they already exist
  def setup_test_database
    drop_and_create_test_database
    drop_and_create_comments_table
  end

  # Creates the ActiveRecord's schema_migrations table required for
  # migrations to work. Before, it drops the table if it already exists
  def drop_and_create_schema_migrations_table
    sql = [
      "USE #{@database}",
      'DROP TABLE IF EXISTS schema_migrations',
      'CREATE TABLE schema_migrations ( version varchar(255) COLLATE utf8_unicode_ci NOT NULL, UNIQUE KEY unique_schema_migrations (version)) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci'
    ]

    run_commands(sql)
  end

  private

  attr_reader :config, :database

  def drop_and_create_test_database
    sql = [
      "DROP DATABASE IF EXISTS #{@database}",
      "CREATE DATABASE #{@database} DEFAULT CHARACTER SET utf8 DEFAULT COLLATE utf8_unicode_ci"
    ]

    run_commands(sql)
  end

  def drop_and_create_comments_table
    sql = [
      "USE #{@database}",
      'DROP TABLE IF EXISTS comments',
      'CREATE TABLE comments ( id bigint(20) NOT NULL AUTO_INCREMENT, PRIMARY KEY (id)) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci'
    ]

    run_commands(sql)
  end

  def run_commands(sql)
    conn.execute('START TRANSACTION')
    sql.each { |str| conn.execute(str) }
    conn.execute('COMMIT')
  end

  def conn
    @conn ||= ActiveRecord::Base.mysql2_connection(
      host: @config['hostname'],
      username: @config['username'],
      password: @config['password'],
      reconnect: true
    )
  end
end