---

name: rails-testing description: This skill should be used when the user asks about testing, test strategy, system tests, integration tests, fixtures, test organization, or Rails testing philosophy. Trigger phrases include "testing", "tests", "fixtures", "system tests", "integration tests", "test strategy", "TDD", "test organization", "Minitest", "test helpers", "factories vs fixtures".

Rails 8 Testing Expert

Expertise in Rails testing philosophy, system tests, fixtures, and test organization for Rails 8 applications.

Core Philosophy: Fixtures Over Factories

Fixtures are fast, predictable, and version controlled. They're the Rails way. Factory Bot adds overhead, complexity, and slower tests. Start with fixtures, stay with fixtures.

Test Types

The Testing Pyramid (Rails Style)

1. System Tests - Full browser simulation, test complete user flows
2. Integration Tests - Controller/request tests without browser
3. Model Tests - Unit tests for business logic
4. Helper/Mailer Tests - Isolated component tests

When to Use Each

Test Type	Use For	Speed
System	Critical user journeys, JS interactions	Slowest
Integration	API endpoints, request/response cycles	Medium
Model	Business logic, validations, scopes	Fastest

System Tests

Setup (Rails 8 Default)

# test/application_system_test_case.rb
class ApplicationSystemTestCase < ActionDispatch::SystemTestCase
  driven_by :selenium, using: :headless_chrome, screen_size: [1400, 1400]
end

Writing System Tests

# test/system/articles_test.rb
require "application_system_test_case"

class ArticlesTest < ApplicationSystemTestCase
  setup do
    @user = users(:steve)
    @article = articles(:rails_guide)
  end

  test "visiting the index" do
    sign_in_as @user
    visit articles_url

    assert_selector "h1", text: "Articles"
    assert_text @article.title
  end

  test "creating an article" do
    sign_in_as @user
    visit new_article_url

    fill_in "Title", with: "New Article"
    fill_in "Body", with: "Article content here"
    click_on "Create Article"

    assert_text "Article created"
    assert_text "New Article"
  end

  test "editing an article with turbo" do
    sign_in_as @user
    visit article_url(@article)

    click_on "Edit"

    within turbo_frame("article_#{@article.id}") do
      fill_in "Title", with: "Updated Title"
      click_on "Save"
    end

    assert_text "Updated Title"
    assert_no_selector "form"  # Frame closed
  end
end

System Test Helpers

# test/support/system_test_helpers.rb
module SystemTestHelpers
  def sign_in_as(user)
    visit login_url
    fill_in "Email", with: user.email
    fill_in "Password", with: "password"
    click_on "Sign in"
    assert_text "Signed in successfully"
  end

  def sign_out
    click_on "Sign out"
    assert_text "Signed out"
  end
end

# Include in test_helper.rb
class ActionDispatch::SystemTestCase
  include SystemTestHelpers
end

Fixtures

Basic Fixtures

# test/fixtures/users.yml
steve:
  name: Steve
  email: steve@example.com
  password_digest: <%= BCrypt::Password.create('password') %>
  admin: false

admin:
  name: Admin User
  email: admin@example.com
  password_digest: <%= BCrypt::Password.create('password') %>
  admin: true

Associations in Fixtures

# test/fixtures/articles.yml
rails_guide:
  title: Getting Started with Rails
  body: Rails is a web framework...
  user: steve  # References users(:steve)
  published_at: <%= 1.day.ago %>

draft_article:
  title: Work in Progress
  body: Not ready yet...
  user: steve
  published_at: null

# test/fixtures/comments.yml
first_comment:
  content: Great article!
  article: rails_guide
  user: admin

Dynamic Fixtures with ERB

# test/fixtures/articles.yml
<% 5.times do |i| %>
article_<%= i %>:
  title: Article <%= i %>
  body: Content for article <%= i %>
  user: steve
  published_at: <%= i.days.ago %>
<% end %>

Why Fixtures Beat Factories

Aspect	Fixtures	Factory Bot
Speed	Fast (loaded once)	Slow (created per test)
Predictability	Same data every run	Generated each time
Database IDs	Fixed, predictable	Random, varying
Setup	None beyond YAML	Gem, config, definitions
Associations	Natural references	Traits, sequences, callbacks

Model Tests

Testing Validations

# test/models/user_test.rb
require "test_helper"

class UserTest < ActiveSupport::TestCase
  test "valid with all attributes" do
    user = User.new(
      name: "Test User",
      email: "test@example.com",
      password: "password"
    )
    assert user.valid?
  end

  test "invalid without email" do
    user = users(:steve)
    user.email = nil
    assert_not user.valid?
    assert_includes user.errors[:email], "can't be blank"
  end

  test "email must be unique" do
    duplicate = User.new(
      name: "Other",
      email: users(:steve).email,
      password: "password"
    )
    assert_not duplicate.valid?
    assert_includes duplicate.errors[:email], "has already been taken"
  end
end

Testing Scopes

test "published scope returns only published articles" do
  published = Article.published

  assert_includes published, articles(:rails_guide)
  assert_not_includes published, articles(:draft_article)
end

test "by_author scope filters by user" do
  steve_articles = Article.by_author(users(:steve))

  assert steve_articles.all? { |a| a.user == users(:steve) }
end

Testing Business Logic

test "completing an order updates status and stock" do
  order = orders(:pending)

  assert_changes -> { order.reload.status }, from: "pending", to: "completed" do
    assert_changes -> { products(:widget).reload.stock_count }, by: -1 do
      order.complete!
    end
  end

  assert_not_nil order.completed_at
end

test "cannot complete already completed order" do
  order = orders(:completed)

  assert_raises Order::AlreadyCompletedError do
    order.complete!
  end
end

Integration/Request Tests

Controller Tests

# test/controllers/articles_controller_test.rb
require "test_helper"

class ArticlesControllerTest < ActionDispatch::IntegrationTest
  setup do
    @article = articles(:rails_guide)
    @user = users(:steve)
  end

  test "should get index" do
    get articles_url
    assert_response :success
    assert_select "h1", "Articles"
  end

  test "should create article when signed in" do
    sign_in_as @user

    assert_difference("Article.count") do
      post articles_url, params: {
        article: { title: "New", body: "Content" }
      }
    end

    assert_redirected_to article_url(Article.last)
  end

  test "should not create article when not signed in" do
    post articles_url, params: {
      article: { title: "New", body: "Content" }
    }

    assert_redirected_to login_url
    assert_equal "Please sign in", flash[:alert]
  end
end

API Tests

# test/controllers/api/articles_controller_test.rb
class Api::ArticlesControllerTest < ActionDispatch::IntegrationTest
  test "returns articles as JSON" do
    get api_articles_url, as: :json

    assert_response :success
    json = JSON.parse(response.body)
    assert_kind_of Array, json
    assert json.any? { |a| a["title"] == articles(:rails_guide).title }
  end

  test "creates article with valid token" do
    post api_articles_url,
      params: { article: { title: "API Article", body: "Content" } },
      headers: { "Authorization" => "Bearer #{api_tokens(:steve).token}" },
      as: :json

    assert_response :created
    assert_equal "API Article", JSON.parse(response.body)["title"]
  end
end

Test Helpers

Shared Setup

# test/test_helper.rb
class ActiveSupport::TestCase
  parallelize(workers: :number_of_processors)
  fixtures :all

  def sign_in_as(user)
    post login_url, params: { email: user.email, password: "password" }
  end
end

Custom Assertions

# test/support/custom_assertions.rb
module CustomAssertions
  def assert_published(article)
    assert article.published?, "Expected article to be published"
    assert_not_nil article.published_at
  end

  def assert_validation_error(record, attribute, message = nil)
    assert_not record.valid?
    if message
      assert_includes record.errors[attribute], message
    else
      assert record.errors[attribute].any?
    end
  end
end

class ActiveSupport::TestCase
  include CustomAssertions
end

Rails 8 Testing Features

Parallel Testing (Default)

# test/test_helper.rb
class ActiveSupport::TestCase
  parallelize(workers: :number_of_processors)
end

Test Transactions

Tests run in transactions and roll back automatically - fixtures are shared, no cleanup needed.

Solid Queue Test Mode

# test/test_helper.rb
class ActiveSupport::TestCase
  include ActiveJob::TestHelper
end

# In tests
test "sends welcome email after signup" do
  assert_enqueued_with(job: WelcomeEmailJob) do
    User.create!(name: "New", email: "new@example.com", password: "password")
  end
end

Anti-Patterns to Avoid

Factory Bot (DON'T)

# Avoid this pattern
FactoryBot.define do
  factory :user do
    sequence(:email) { |n| "user#{n}@example.com" }
    password { "password" }
  end
end

# Every test creates new records - slow!
let(:user) { create(:user) }

Testing Implementation, Not Behavior (DON'T)

# BAD: Testing internal implementation
test "calls send_email method" do
  user = users(:steve)
  mock = Minitest::Mock.new
  mock.expect :call, true

  User.stub :send_email, mock do
    user.welcome!
  end

  mock.verify
end

# GOOD: Testing behavior
test "welcome sends email" do
  assert_emails 1 do
    users(:steve).welcome!
  end
end

Test Organization

test/
├── test_helper.rb
├── application_system_test_case.rb
├── fixtures/
│   ├── users.yml
│   └── articles.yml
├── models/
│   ├── user_test.rb
│   └── article_test.rb
├── controllers/
│   └── articles_controller_test.rb
├── system/
│   └── articles_test.rb
├── integration/
│   └── user_flows_test.rb
└── support/
    ├── system_test_helpers.rb
    └── custom_assertions.rb

Running Tests

bin/rails test                    # All tests except system
bin/rails test:system             # System tests only
bin/rails test:all                # Everything
bin/rails test test/models        # Just model tests
bin/rails test test/models/user_test.rb:25  # Specific line

Additional Resources

• references/fixtures-guide.md - Advanced fixture patterns
• references/system-tests.md - Browser testing patterns
• examples/model-test.rb - Complete model test
• examples/system-test.rb - System test patterns