Rails 6 + Shoulda matchers + minitest-matchers_vaccine

steps.sh

gem install rails -v 6.0.0.beta3
rails _6.0.0.beta3_ new shoulda-matchers_test
bin/rails g scaffold User username:string
rails db:migrate RAILS_ENV=test

# Add the following gems to the test group
gem 'shoulda-matchers', git: 'https://github.com/thoughtbot/shoulda-matchers.git' # Required for Rails 6 (https://github.com/thoughtbot/shoulda-matchers/pull/1193)
gem 'minitest-matchers_vaccine'

# Add some validation to the user model, see user.rb

# Update the user test, see user_test.rb

bin/rails test test/models/user_test.rb # Fails because of an "undefined method `validate_presence_of'"

# Uncomment the fourth line in user_test.rb to include the ActiveModel matchers manually.

bin/rails test test/models/user_test.rb # Success

user.rb

class User < ApplicationRecord
  validates :username, presence: true
end

user_test.rb

require 'test_helper'

class UserTest < ActiveSupport::TestCase
  # include Shoulda::Matchers::ActiveModel

  setup do
    @subject = User.new
  end

  test 'validations and associations' do
    must validate_presence_of(:username)
  end
end