System tests with Capybara in Ruby on Rails - Mini Project: Build & Apply

System tests with Capybara

📖 Scenario: You are building a simple blog application in Rails. You want to make sure that users can visit the homepage and see the welcome message correctly.

🎯 Goal: Create a system test using Capybara that visits the homepage and checks for the presence of the welcome text.

📋 What You'll Learn

Create a system test file for the homepage

Set up Capybara to visit the root path

Write a test that checks for the welcome message text

Run the test to verify it passes

💡 Why This Matters

🌍 Real World

System tests help ensure your web app works correctly from the user's point of view by simulating real browser actions.

💼 Career

Knowing how to write system tests with Capybara is valuable for Rails developers to maintain high-quality, reliable applications.

1

Create the system test file

Create a system test file called home_page_test.rb inside test/system/ folder with a class HomePageTest that inherits from ApplicationSystemTestCase.

Ruby on Rails

# Your code here

Hint

This file sets up the system test class where you will write your tests.

2

Add a test method to visit the homepage

Inside the HomePageTest class, add a test method called test_visiting_homepage that uses visit root_path to open the homepage.

Ruby on Rails

require "application_system_test_case"

class HomePageTest < ApplicationSystemTestCase
  # Add test method to visit homepage
end

Hint

The visit method tells Capybara to open the page at the given path.

3

Check for the welcome message on the homepage

Inside the test_visiting_homepage method, add an assertion using assert_text "Welcome to the Blog!" to verify the welcome message is visible.

Ruby on Rails

require "application_system_test_case"

class HomePageTest < ApplicationSystemTestCase
  test "visiting homepage" do
    visit root_path
    # Add assertion to check welcome message
  end
end

Hint

The assert_text method checks if the given text appears anywhere on the page.

4

Run the system test

Run the system test by executing bin/rails test:system test/system/home_page_test.rb in your terminal to verify the test passes.

Ruby on Rails

# Run the system test in terminal
# Your code here

Hint

Use the Rails command line to run system tests and see the results.

Practice

1. What is the main purpose of system tests with Capybara in a Rails application?

easy

A. To test individual Ruby methods for correctness

B. To measure server response time under load

C. To check database schema migrations

D. To simulate user actions in a real browser and check app behavior

Solution

1. Step 1: Understand system tests role

   System tests simulate how a real user interacts with the app through a browser.

2. Step 2: Compare with other test types

   Unlike unit tests or performance tests, system tests focus on full app behavior with UI.

3. Final Answer:

   To simulate user actions in a real browser and check app behavior -> Option D

4. Quick Check:

   System tests = simulate user in browser [OK]

Hint: System tests mimic real user clicks and typing [OK]

Common Mistakes:

• Confusing system tests with unit tests
• Thinking system tests check only backend code
• Assuming system tests measure performance

2. Which of the following is the correct way to visit the homepage in a Capybara system test?

easy

A. navigate_to root_url

B. go_to '/'

C. visit root_path

D. open_page '/'

Solution

1. Step 1: Recall Capybara visit syntax

   Capybara uses the method visit with a path or URL to open a page.

2. Step 2: Match correct method and argument

   root_path is the Rails helper for homepage path, so visit root_path is correct.

3. Final Answer:

   visit root_path -> Option C

4. Quick Check:

   Capybara visit + path helper = visit root_path [OK]

Hint: Use 'visit' with Rails path helpers to open pages [OK]

Common Mistakes:

• Using non-existent methods like go_to or open_page
• Confusing root_path with root_url in system tests
• Forgetting to use visit before path

3. Given this system test code snippet, what will be the output on the page?

visit root_path
fill_in 'Email', with: '[e-mail]'
fill_in 'Password', with: 'secret'
click_button 'Log in'
expect(page).to have_content('Welcome, [e-mail]')

medium

A. Test passes if 'Welcome, [e-mail]' appears after login

B. Test fails because 'fill_in' cannot find fields

C. Test raises error due to missing 'visit' method

D. Test passes without checking page content

Solution

1. Step 1: Analyze test steps

   The test visits the homepage, fills in login form fields, clicks login, then checks for welcome message.

2. Step 2: Understand Capybara behavior

   If the login works and page shows the welcome text, have_content will pass and test passes.

3. Final Answer:

   Test passes if 'Welcome, [e-mail]' appears after login -> Option A

4. Quick Check:

   fill_in + click_button + have_content = success check [OK]

Hint: Check page content after actions to confirm success [OK]

Common Mistakes:

• Assuming fill_in fails without checking form existence
• Forgetting to call visit before actions
• Ignoring the expect(page).to have_content assertion

4. You wrote this system test but it fails with "Capybara::ElementNotFound" error:

visit root_path
fill_in 'Username', with: 'testuser'
click_button 'Submit'

What is the most likely cause?

medium

A. Capybara does not support fill_in method

B. The form does not have a field labeled 'Username'

C. The button 'Submit' is missing from the page

D. You forgot to call visit before fill_in

Solution

1. Step 1: Understand Capybara::ElementNotFound meaning

   This error means Capybara could not find the form field or button with given label.

2. Step 2: Check test code and error cause

   Since visit is called, the likely cause is the field labeled 'Username' does not exist on the page.

3. Final Answer:

   The form does not have a field labeled 'Username' -> Option B

4. Quick Check:

   ElementNotFound = missing field or button [OK]

Hint: Check labels exactly match form fields and buttons [OK]

Common Mistakes:

• Assuming visit was not called when it was
• Thinking Capybara lacks fill_in support
• Ignoring exact label spelling and case

5. You want to write a system test that logs in a user, visits their profile page, and verifies their username is shown. Which sequence correctly uses Capybara commands?

hard

A. visit login_path; fill_in 'Email', with: user.email; fill_in 'Password', with: user.password; click_button 'Log in'; visit profile_path(user); expect(page).to have_content(user.username)

B. fill_in 'Email', with: user.email; click_button 'Log in'; visit profile_path(user); expect(page).to have_content(user.username)

C. visit profile_path(user); fill_in 'Email', with: user.email; click_button 'Log in'; expect(page).to have_content(user.username)

D. visit login_path; click_button 'Log in'; fill_in 'Email', with: user.email; fill_in 'Password', with: user.password; expect(page).to have_content(user.username)

Solution

1. Step 1: Identify correct login flow

   You must visit the login page first, then fill in email and password, then click login.

2. Step 2: Visit profile after login and check content

   After successful login, visit the profile page and check the username is displayed.

3. Final Answer:

   visit login_path; fill_in 'Email', with: user.email; fill_in 'Password', with: user.password; click_button 'Log in'; visit profile_path(user); expect(page).to have_content(user.username) -> Option A

4. Quick Check:

   Login then visit profile then check content [OK]

Hint: Always visit pages before interacting or checking content [OK]

Common Mistakes:

• Trying to fill_in before visiting login page
• Visiting profile before logging in
• Clicking buttons before filling required fields