Rails ActiveSupport::TestCase helper method for checking a model record has an error on a field

active record error on field test.rb

# This method allows you to not have to hardcode validation messages as a part of unit 
# tests, instead relying, as the ActiveModel::Errors class does, on I18n dictionaries.
# Usage: assert_has_error(@new_user, :first_name, :regexp)
#   Of course, in the above example, :regexp is a custom type of error that I implemented
#   for my own app, but you can substitute things like :invalid, :blank, :inclusion, etc.

def assert_has_error(record, attribute, type = :invalid)
  record.send(:run_validations!) # This in order to trigger the :validate callback first.
  assert record.errors[attribute].include?(record.errors.generate_message(attribute, type)), "Expected #{record.class.model_name.human} record to have an error of type :#{type} for attribute #{record.class.human_attribute_name(attribute)}."
end