testing

test/
├── test_helper.rb                    # Global config
├── application_system_test_case.rb   # System test base (created on first system test)
├── controllers/                      # Controller/functional tests (legacy — prefer request tests)
├── fixtures/                         # YAML fixture data
│   ├── users.yml
│   ├── files/                        # File fixtures for uploads
│   └── action_text/rich_texts.yml    # Action Text fixtures
├── helpers/                          # View helper tests
├── integration/                      # Integration tests
├── jobs/                             # Job tests
├── mailers/                          # Mailer tests
│   └── previews/                     # Mailer previews (not tests, but useful)
├── models/                           # Model tests (bulk of your tests)
├── channels/                         # Action Cable channel tests
│   └── application_cable/            # Connection tests
├── requests/                         # Request tests (preferred over controllers/)
├── services/                         # Service object tests
├── system/                           # System tests (keep small)
└── support/                          # Shared test helpers

# Run everything (excludes system tests)
bin/rails test
 
# Run system tests separately
bin/rails test:system
 
# Run ALL tests including system
bin/rails test:all
 
# Run a single file
bin/rails test test/models/user_test.rb
 
# Run a specific test by line number
bin/rails test test/models/user_test.rb:42
 
# Run a line range
bin/rails test test/models/user_test.rb:10-30
 
# Run by name pattern
bin/rails test -n /password/
 
# Run a directory
bin/rails test test/models/
 
# Fail fast — stop on first failure
bin/rails test --fail-fast
 
# Verbose output
bin/rails test -v
 
# Profile slow tests
bin/rails test --profile
 
# Set seed for reproducibility
bin/rails test --seed 12345

class ArticlesRequestTest < ActionDispatch::IntegrationTest
  setup do
    @user = users(:admin)
    @article = articles(:published)
  end
 
  test "GET /articles returns success" do
    get articles_url
    assert_response :success
  end
 
  test "POST /articles creates with valid params" do
    sign_in @user
    assert_difference "Article.count", 1 do
      post articles_url, params: { article: { title: "New", body: "Content" } }
    end
    assert_redirected_to article_url(Article.last)
  end
 
  test "POST /articles rejects invalid params" do
    sign_in @user
    assert_no_difference "Article.count" do
      post articles_url, params: { article: { title: "" } }
    end
    assert_response :unprocessable_entity
  end
end

# test/application_system_test_case.rb
require "test_helper"
 
class ApplicationSystemTestCase < ActionDispatch::SystemTestCase
  driven_by :selenium, using: :headless_chrome
end

require "application_system_test_case"
 
class CheckoutTest < ApplicationSystemTestCase
  test "user completes checkout" do
    user = users(:buyer)
    product = products(:widget)
 
    visit new_session_path
    fill_in "Email", with: user.email
    fill_in "Password", with: "password"
    click_on "Sign in"
 
    visit product_path(product)
    click_on "Add to Cart"
    click_on "Checkout"
 
    fill_in "Card number", with: "4242424242424242"
    click_on "Pay"
 
    assert_text "Order confirmed"
  end
end

class UserMailerTest < ActionMailer::TestCase
  test "welcome email" do
    email = UserMailer.welcome(users(:new_user))
    assert_emails 1 do
      email.deliver_now
    end
    assert_equal ["noreply@example.com"], email.from
    assert_equal [users(:new_user).email], email.to
    assert_equal "Welcome!", email.subject
    assert_match users(:new_user).name, email.body.to_s
  end
end

class ProcessOrderJobTest < ActiveJob::TestCase
  test "charges the account" do
    perform_enqueued_jobs do
      ProcessOrderJob.perform_later(orders(:pending))
    end
    assert orders(:pending).reload.charged?
  end
end

class OrderTest < ActiveSupport::TestCase
  include ActiveJob::TestHelper
 
  test "#place enqueues processing job" do
    assert_enqueued_with(job: ProcessOrderJob) do
      orders(:new).place!
    end
  end
end

class CurrencyHelperTest < ActionView::TestCase
  test "formats USD" do
    assert_equal "$10.00", format_price(1000, "USD")
  end
 
  test "handles zero" do
    assert_equal "$0.00", format_price(0, "USD")
  end
end

# Channel test
class ChatChannelTest < ActionCable::Channel::TestCase
  test "subscribes to room stream" do
    subscribe room: "general"
    assert subscription.confirmed?
    assert_has_stream "chat_general"
  end
end
 
# Connection test
class ApplicationCable::ConnectionTest < ActionCable::Connection::TestCase
  test "connects with valid user" do
    cookies.signed[:user_id] = users(:admin).id
    connect
    assert_equal users(:admin).id, connection.current_user.id
  end
 
  test "rejects without auth" do
    assert_reject_connection { connect }
  end
end

# After migrations, sync test DB schema
bin/rails db:test:prepare
 
# Or recreate from scratch
bin/rails db:test:purge db:test:prepare
 
# Rails auto-checks for pending migrations before tests run

class ThreadedTest < ActiveSupport::TestCase
  self.use_transactional_tests = false
 
  teardown do
    # Manual cleanup needed!
    User.delete_all
  end
end

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

# Override worker count
PARALLEL_WORKERS=4 bin/rails test

class ActiveSupport::TestCase
  parallelize(workers: :number_of_processors, with: :threads)
end

# config/environments/test.rb
config.eager_load = ENV["CI"].present?

# CI steps
bin/rails db:test:prepare
bin/rails test                    # Unit + request tests
bin/rails test:system             # System tests (separate job recommended)

freeze_time do ... end                                    # Freeze at current moment
travel_to Time.zone.local(2024, 1, 15) do ... end        # Travel to specific time
travel 3.days do ... end                                  # Travel forward
travel_back                                               # Return to real time