Controller tests in Ruby on Rails - Mini Project: Build & Apply

Basic Controller Tests in Rails

📖 Scenario: You are building a simple blog application in Rails. You want to make sure your PostsController works correctly by writing tests for its main actions.

🎯 Goal: Write controller tests for the PostsController to check that the index and show actions respond successfully and render the correct templates.

📋 What You'll Learn

Create a test file for PostsController in test/controllers/posts_controller_test.rb

Write a test for the index action that checks for a successful HTTP response

Write a test for the show action that checks for a successful HTTP response

Use Rails built-in test framework syntax

💡 Why This Matters

🌍 Real World

Controller tests help ensure that your web app's pages load correctly and respond as expected before you deploy your app.

💼 Career

Writing controller tests is a common task for Rails developers to maintain code quality and prevent bugs in web applications.

1

Setup test data

Create a Post record in the test database with title set to 'Test Post' and body set to 'This is a test post.'. Write this inside the setup method of PostsControllerTest.

Ruby on Rails

require "test_helper"

class PostsControllerTest < ActionDispatch::IntegrationTest
  def setup
    # Create a Post record with title 'Test Post' and body 'This is a test post.'
    # Your code here
  end
end

Hint

Use Post.create inside the setup method to create the test post.

2

Test the index action response

Add a test method called test_index_should_get_success that sends a get request to posts_url and asserts the response is successful using assert_response :success.

Ruby on Rails

require "test_helper"

class PostsControllerTest < ActionDispatch::IntegrationTest
  def setup
    @post = Post.create(title: "Test Post", body: "This is a test post.")
  end

  # Add a test for index action response
  # Your code here
end

Hint

Use get posts_url and then assert_response :success inside the test method.

3

Test the show action response

Add a test method called test_show_should_get_success that sends a get request to post_url(@post) and asserts the response is successful using assert_response :success.

Ruby on Rails

require "test_helper"

class PostsControllerTest < ActionDispatch::IntegrationTest
  def setup
    @post = Post.create(title: "Test Post", body: "This is a test post.")
  end

  def test_index_should_get_success
    get posts_url
    assert_response :success
  end

  # Add a test for show action response
  # Your code here
end

Hint

Use get post_url(@post) and assert_response :success inside the test method.

4

Complete the test file

Ensure the test file test/controllers/posts_controller_test.rb includes the setup method and both test methods test_index_should_get_success and test_show_should_get_success inside the PostsControllerTest class.

Ruby on Rails

require "test_helper"

class PostsControllerTest < ActionDispatch::IntegrationTest
  def setup
    @post = Post.create(title: "Test Post", body: "This is a test post.")
  end

  def test_index_should_get_success
    get posts_url
    assert_response :success
  end

  def test_show_should_get_success
    get post_url(@post)
    assert_response :success
  end

  # Confirm the class is closed properly
  # Your code here
end

Hint

Make sure the class and methods are properly closed with end.

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