`on`で指定したcontextの時にだけ、html5 validationを有効にしたいケースのサンプルコード

sample.rb

require "bundler/inline"

gemfile do
  source "https://rubygems.org"

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

  gem "rails"
  gem "html5_validators"
  gem "sqlite3"
end

require "action_controller/railtie"

class TaskApp < Rails::Application
  Rails.logger = Logger.new $stdout
  secrets.secret_key_base = "secret_key_base"
  config.eager_load = false

  initialize!

  routes.draw do
    resources :tasks, only: [:new, :create, :edit, :update]
  end
end

require "active_record"

ActiveRecord::Base.establish_connection adapter: "sqlite3", database: ":memory:"
ActiveRecord::Schema.define do
  create_table :tasks, force: true do |t|
    t.string :name
    t.text :memo
  end
end

class Task < ActiveRecord::Base
  validates :name, presence: true
  validates :memo, presence: true, on: :update
end

class TasksController < ActionController::Base
  TEMPLATE =<<~ERB
    <%= form_for @task do |f| %>
    <%= f.text_field :name %>
    <%= f.text_area :memo %>
    <% end %>
  ERB

  def new
    @task = Task.new
    render inline: TEMPLATE
  end

  def edit
    @task = Task.find(params[:id])
    render inline: TEMPLATE
  end
end

require "minitest/autorun"
require "rack/test"

class TasksTest < Minitest::Test
  include Rack::Test::Methods

  def test_only_add_required_attribute_on_create
    get "/tasks/new"

    assert_match %r{<input required="required" type="text" name="task\[name\]" id="task_name" />}, last_response.body
    # 現在は `<textarea required="required" name="task[memo]" ...` と、updateのcontextだけで有効にしたいケース以外でもhtml5 validationsが有効になる
    assert_match %r{<textarea name="task\[memo\]" id="task_memo">\n</textarea>}, last_response.body
  end

  def test_only_add_required_attribute_on_update
    Task.create name: "foo"

    get "/tasks/1/edit"

    assert_match %r{<input required="required" type="text" value="foo" name="task\[name\]" id="task_name" />}, last_response.body
    assert_match %r{<textarea required="required" name="task\[memo\]" id="task_memo">\n</textarea>}, last_response.body
  end

  private

  def app
    TaskApp
  end
end