Controller tests in Ruby on Rails - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What is the output of this Rails controller test?

Given the following test for a Rails controller action, what will be the test result?

Ruby on Rails

require 'rails_helper'

RSpec.describe ArticlesController, type: :controller do
  describe 'GET #show' do
    let(:article) { Article.create(title: 'Test', content: 'Content') }

    it 'returns a successful response' do
      get :show, params: { id: article.id }
      expect(response).to have_http_status(:success)
    end
  end
end

A The test fails with a routing error because the route is missing.

B The test fails because the article is not saved to the database.

C The test passes because the show action returns HTTP status 200.

D The test raises a syntax error due to missing end keywords.

💡 Hint

Check if the article is created and the show action is called correctly.

The test creates an article and calls the show action with its id. The response should be successful (HTTP 200).

❓ state_output

intermediate

What is the value of flash[:notice] after this controller test runs?

Consider this controller test snippet. What will be the value of flash[:notice] after the POST create action?

Ruby on Rails

RSpec.describe PostsController, type: :controller do
  describe 'POST #create' do
    it 'sets a flash notice on success' do
      post :create, params: { post: { title: 'Hello', body: 'World' } }
      # What is flash[:notice] here?
    end
  end
end

# Controller code:
# def create
#   @post = Post.new(post_params)
#   if @post.save
#     flash[:notice] = 'Post was successfully created.'
#     redirect_to @post
#   else
#     render :new
#   end
# end

A 'Error creating post.'

B 'Post was successfully created.'

C nil

D Raises a NoMethodError

💡 Hint

The post is created with valid parameters, so the success branch runs.

Since the post saves successfully, flash[:notice] is set to the success message.

🔧 Debug

advanced

Why does this controller test raise an error?

This test raises an error when run. What is the cause?

Ruby on Rails

RSpec.describe UsersController, type: :controller do
  describe 'DELETE #destroy' do
    it 'deletes the user' do
      user = User.create(name: 'Alice')
      delete :destroy, params: { id: user.id }
      expect(User.find_by(id: user.id)).to be_nil
    end
  end
end

# Controller code:
# def destroy
#   User.find(params[:id]).destroy
#   redirect_to users_path
# end

A The test raises ActiveRecord::RecordNotFound because User.find(user.id) fails after deletion.

B The test raises a NoMethodError because destroy is undefined.

C The test fails because the user is not created before the test.

D The test raises a routing error due to missing route.

💡 Hint

Check what happens when you try to find a deleted record.

After deletion, User.find(user.id) raises ActiveRecord::RecordNotFound because the record no longer exists.

📝 Syntax

advanced

Which option fixes the syntax error in this controller test?

Identify the correct syntax to test a PATCH update action in Rails controller tests.

Ruby on Rails

RSpec.describe CommentsController, type: :controller do
  describe 'PATCH #update' do
    let(:comment) { Comment.create(body: 'Old') }

    it 'updates the comment body' do
      patch :update, params: { id: comment.id, comment: { body: 'New' } }
      comment.reload
      expect(comment.body).to eq('New')
    end
  end
end

A patch :update, params: { id: comment.id, comment: { body: 'New' } }

B patch update, params: { id: comment.id, comment: { body: 'New' } }

C patch :update, id: comment.id, comment: { body: 'New' }

D patch :update, { id: comment.id, comment: { body: 'New' } }

💡 Hint

The params hash must be passed with the key :params.

Option A uses the correct syntax with :update and params hash. Other options have syntax errors or missing keys.

🧠 Conceptual

expert

Which option best describes the purpose of controller tests in Rails?

Select the statement that most accurately explains why we write controller tests in Rails applications.

A To test the database schema and ensure migrations run without errors.

B To replace integration tests by testing all user flows in one place.

C To check the styling and layout of views rendered by the controller.

D To verify that controller actions respond correctly to HTTP requests and manipulate data as expected.

💡 Hint

Think about what controllers do in a Rails app and what tests should confirm.

Controller tests check that actions handle requests properly, return correct responses, and change data as intended.