AssertValid

A tiny gem that provides that provides two utility methods for testing ActiveRecord models: assert_valid and assert_invalid.

This gem could easily just be a GitHub gist—the methods are written in less than 50 lines.

But I've copy and pasted them enough times that I just made a gem.

Add this gem to your Rails app's development group:

group :test do
  # ...
  gem 'assert_valid'
end

And then bundle install.

Include the module in test/test_helper.rb:

class ActiveSupport::TestCase
  include AssertValid::Assertions
  # ...

Or instead of using the gem, you could just copy the methods as defined in lib/assert_valid/assertions.rb and paste them into your test/test_helper.rb.

In your unit tests, you can use assert_valid or assert_invalid, passing in the record you want to check.

assert_invalid also optionally takes an attribute name to check for an error on that attribute specifically.

If you specify an attribute, you can also specify an error kind. Example:

# app/models/user.rb
class User < ApplicationRecord
  validates :name, uniqueness: true
  #...
  

# test/models/user_test.rb

test "validates unique name" do
  User.create(name: "bob")
  duplicated_user = User.new(name: "bob")
  assert_invalid(duplicated_user, :name, :taken)

The gem is available as open source under the terms of the MIT License.