Issue in rails 5.2.1 introduced with commit https://github.com/rails/rails/commit/c15d8b3a21bf1ae3ca9f09ca9cad8cc3828aa9be?diff=split

active_record_gem.rb

# frozen_string_literal: true

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"

  git_source(:github) { |repo| "https://github.com/#{repo}.git" }

  # Activate the gem you are reporting the issue against.
  gem "activerecord", "5.2.1"
  gem "actionview", "5.2.1"
  gem "sqlite3"
end

require "active_record"
require "action_view"
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 :posts, force: true do |t|
    t.float :price
  end
end

class Post < ActiveRecord::Base
  include ActionView::Helpers::NumberHelper
  validates :price, numericality: true

  def price
    number_to_currency self[:price]
  end
end

class BugTest < Minitest::Test
  def test_association_stuff
    post = Post.create!(price: 1.5)
    assert post.valid?
  end
end