Controller tests in Ruby on Rails

Introduction

Controller tests check if your app's web pages and actions work correctly. They make sure the right pages show up and the right data is handled.

When you want to verify a web page loads successfully.

When you need to check if submitting a form triggers the correct action.

When you want to confirm redirects happen as expected.

When you want to test if the controller assigns the right data to views.

When you want to catch errors early before users see them.

Syntax

Ruby on Rails

test "description" do
  get :action_name
  assert_response :success
  assert_not_nil assigns(:variable)
end

Use get, post, patch, delete to simulate HTTP requests.

assert_response checks the HTTP status like success or redirect.

Examples

This test checks if the index page loads without errors.

Ruby on Rails

test "should get index" do
  get :index
  assert_response :success
end

This test submits data to create an item and checks if it redirects to the item's page.

Ruby on Rails

test "should redirect after create" do
  post :create, params: { item: { name: "Book" } }
  assert_redirected_to item_path(assigns(:item))
end

This test ensures the controller sets the @items variable for the view.

Ruby on Rails

test "should assign items" do
  get :index
  assert_not_nil assigns(:items)
end

Sample Program

This test file checks two things: the index page loads and the create action adds a book then redirects properly.

Ruby on Rails

require "test_helper"

class BooksControllerTest < ActionController::TestCase
  test "should get index" do
    get :index
    assert_response :success
    assert_not_nil assigns(:books)
  end

  test "should create book and redirect" do
    post :create, params: { book: { title: "Rails Guide" } }
    assert_redirected_to book_path(assigns(:book))
  end
end

Important Notes

Controller tests run fast and help catch mistakes early.

Use assigns(:variable) to check variables sent to views.

Remember to test both success and failure cases for actions.

Summary

Controller tests check if web requests work as expected.

Use HTTP verbs like get and post to simulate user actions.

Check responses, redirects, and assigned variables to ensure correct behavior.

Practice

1. What is the main purpose of a controller test in Rails?

easy

A. To check if web requests respond correctly and perform expected actions

B. To test database schema changes

C. To verify CSS styles are applied properly

D. To check JavaScript functions run without errors

Solution

1. Step 1: Understand controller test role

   Controller tests simulate web requests to check if the controller responds correctly.

2. Step 2: Compare options

   Only To check if web requests respond correctly and perform expected actions describes checking web requests and expected actions, which is the controller test's purpose.

3. Final Answer:

   To check if web requests respond correctly and perform expected actions -> Option A

4. Quick Check:

   Controller tests check web requests = A [OK]

Hint: Controller tests simulate web requests to check responses [OK]

Common Mistakes:

• Confusing controller tests with database or view tests
• Thinking controller tests check CSS or JavaScript
• Assuming controller tests modify database schema

2. Which of the following is the correct syntax to simulate a GET request to the index action in a Rails controller test?

easy

A. get('/index')

B. get index

C. get index()

D. get :index

Solution

1. Step 1: Recall Rails controller test syntax

   In Rails controller tests, the correct way to simulate a GET request is using get :action_name.

2. Step 2: Analyze options

   get :index uses get :index, which is correct syntax. Others are invalid or incorrect Ruby syntax.

3. Final Answer:

   get :index -> Option D

4. Quick Check:

   Use symbol with get method = C [OK]

Hint: Use get :action_name with a symbol for controller tests [OK]

Common Mistakes:

• Using string or method call syntax instead of symbol
• Omitting colon before action name
• Using parentheses incorrectly

3. Given this controller test snippet:

get :show, params: { id: 1 }
assert_response :success
assert_not_nil assigns(:user)

What does assert_not_nil assigns(:user) check?

medium

A. That the @user variable was assigned in the controller

B. That the user with id 1 exists in the database

C. That the response body contains the word 'user'

D. That the controller redirected to the user page

Solution

1. Step 1: Understand assigns method in controller tests

   The assigns(:user) method accesses the instance variable @user set by the controller.

2. Step 2: Interpret assert_not_nil usage

   assert_not_nil assigns(:user) checks that @user is not nil, meaning it was assigned.

3. Final Answer:

   That the @user variable was assigned in the controller -> Option A

4. Quick Check:

   assigns(:user) checks @user variable = B [OK]

Hint: assigns(:var) checks controller instance variable @var [OK]

Common Mistakes:

• Thinking assigns checks database existence
• Confusing assigns with response content
• Assuming assigns checks redirects

4. Identify the error in this Rails controller test code:

post :create, user: { name: 'Alice' }
assert_redirected_to user_path(assigns(:user))

medium

A. assert_redirected_to should be assert_response

B. Using post instead of get for create action

C. Missing params: keyword before user hash in post request

D. assigns(:user) cannot be used in controller tests

Solution

1. Step 1: Check syntax for post request with parameters

   In Rails 5+, parameters must be wrapped inside params: keyword.

2. Step 2: Analyze given code

   The code uses post :create, user: { name: 'Alice' } missing params:, causing syntax error.

3. Final Answer:

   Missing params: keyword before user hash in post request -> Option C

4. Quick Check:

   Use params: for parameters in post requests = A [OK]

Hint: Always use params: keyword for request parameters [OK]

Common Mistakes:

• Omitting params: keyword in request methods
• Confusing HTTP verbs for actions
• Misusing assertion methods

5. You want to test that after creating a new user, the controller redirects to the user's show page and sets a flash notice. Which test code correctly checks both behaviors?

hard

A. post :create, params: { user: { name: 'Bob' } }
assert_response :redirect
assert_nil flash[:notice]

B. post :create, params: { user: { name: 'Bob' } }
assert_redirected_to user_path(assigns(:user))
assert_equal 'User created!', flash[:notice]

C. get :create, params: { user: { name: 'Bob' } }
assert_redirected_to user_path(assigns(:user))
assert flash[:alert] == 'User created!'

D. post :create, user: { name: 'Bob' }
assert_response :success
assert flash[:notice] == 'User created!'

Solution

1. Step 1: Check HTTP verb and parameters

   Creating a user uses POST with params: keyword, so post :create, params: { user: { name: 'Bob' } } assert_redirected_to user_path(assigns(:user)) assert_equal 'User created!', flash[:notice] is correct here.

2. Step 2: Verify assertions for redirect and flash

   post :create, params: { user: { name: 'Bob' } } assert_redirected_to user_path(assigns(:user)) assert_equal 'User created!', flash[:notice] asserts redirect to user's show page and flash notice equals 'User created!'. This matches the requirement.

3. Step 3: Eliminate incorrect options

   post :create, user: { name: 'Bob' } assert_response :success assert flash[:notice] == 'User created!' misses params: keyword and uses assert_response :success instead of redirect. get :create, params: { user: { name: 'Bob' } } assert_redirected_to user_path(assigns(:user)) assert flash[:alert] == 'User created!' uses GET instead of POST and wrong flash key. post :create, params: { user: { name: 'Bob' } } assert_response :redirect assert_nil flash[:notice] asserts flash[:notice] is nil, which is wrong.

4. Final Answer:

   post :create, params: { user: { name: 'Bob' } } assert_redirected_to user_path(assigns(:user)) assert_equal 'User created!', flash[:notice] -> Option B

5. Quick Check:

   POST with params, redirect, and flash notice = D [OK]

Hint: Use post with params:, assert_redirected_to, and assert_equal flash [OK]

Common Mistakes:

• Using get instead of post for create action
• Forgetting params: keyword
• Checking wrong flash key or missing redirect assertion