Gist for https://github.com/rails/rails/issues/26437

inline_migration_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", "5.0.0.1"
  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::Schema.define do
  create_table :payment_logs, force: true do |t|
    t.decimal :amount, precision: 10, scale: 0, default: 0, null: false
  end
end

class PaymentLog < ActiveRecord::Base

end


class ChangeAmountToAddScale < ActiveRecord::Migration[5.0]
  def change
    reversible do |dir|
      dir.up do
        change_column :payment_logs, :amount, :decimal, precision: 10, scale: 2, default: 0, null: false
      end

      dir.down do
        change_column :payment_logs, :amount, :decimal, precision: 10, scale: 0, default: 0, null: false
      end
    end
  end
end


class BugTest < Minitest::Test

  def test_migrations
    migrator = ActiveRecord::Migrator.new(:up, [ChangeAmountToAddScale])
    migrator.run
    PaymentLog.reset_column_information
    assert_equal "decimal(10,2)", PaymentLog.columns.last.sql_type

    migrator = ActiveRecord::Migrator.new(:down, [ChangeAmountToAddScale])
    migrator.run
    PaymentLog.reset_column_information
    assert_equal "decimal(10,0)", PaymentLog.columns.last.sql_type
  end

end