System tests with Capybara in Ruby on Rails - Step-by-Step Execution

Concept Flow - System tests with Capybara

Start Test Suite

↓

Setup Test Environment

↓

Launch Browser Simulator

↓

Visit Web Page

↓

Find Elements & Interact

↓

Check Expected Outcomes

↓

Pass or Fail Test

↓

Close Browser Simulator

↓

End Test Suite

This flow shows how a system test with Capybara runs: it sets up, opens a simulated browser, visits pages, interacts with elements, checks results, and finishes.

Execution Sample

Ruby on Rails

require "application_system_test_case"

class HomePageTest < ApplicationSystemTestCase
  test "visiting the home page" do
    visit "/"
    assert_selector "h1", text: "Welcome"
  end
end

This test opens the home page and checks if an <h1> with 'Welcome' text is present.

Execution Table

Step	Action	Evaluation	Result
1	Start test 'visiting the home page'	N/A	Test begins
2	Setup test environment	N/A	Test environment ready
3	Launch browser simulator	N/A	Browser simulator opened
4	Visit '/' page	N/A	Home page loaded
5	Find <h1> element with text 'Welcome'	Element found?	Yes, element found
6	Assert element text equals 'Welcome'	Text matches?	Yes, assertion passes
7	Test passes	N/A	Test marked as passed
8	Close browser simulator	N/A	Browser closed
9	End test	N/A	Test suite ends

💡 Test ends after assertion passes and browser simulator closes

Variable Tracker

Variable	Start	After Step 4	After Step 5	After Step 6	Final
page_url	nil	"/"	"/"	"/"	"/"
element_found	false	false	true	true	true
assertion_passed	false	false	false	true	true

Key Moments - 3 Insights

Why do we need to launch a browser simulator in system tests?

Because Capybara simulates a real user interacting with the app through a browser, so launching a browser simulator lets the test behave like a real user. See execution_table step 3.

What happens if the <h1> element with text 'Welcome' is not found?

The assertion fails at step 6, causing the test to fail and stop. The test won't reach step 7 or beyond.

Why do we close the browser simulator at the end?

To clean up resources and avoid leftover browser processes. This happens at step 8 to keep tests isolated and efficient.

Visual Quiz - 3 Questions

Look at the execution table, what is the value of 'element_found' after step 5?

A true

B false

C nil

D undefined

💡 Hint

Check variable_tracker row for 'element_found' at 'After Step 5'

At which step does the test confirm the page has loaded?

A Step 2

B Step 4

C Step 6

D Step 8

💡 Hint

Look at execution_table action descriptions for page loading

If the assertion fails, which step would the test NOT reach?

A Step 5

B Step 6

C Step 7

D Step 4

💡 Hint

See execution_table steps after assertion passes

Concept Snapshot

System tests with Capybara simulate user actions in a browser.
Use 'visit' to open pages and 'assert_selector' to check elements.
Tests run in a browser simulator for realistic interaction.
Close the simulator after tests to clean up.
Assertions decide if tests pass or fail.

Full Transcript

System tests with Capybara run by starting a test, setting up the environment, and launching a browser simulator. The test visits a web page, finds elements like headers, and checks if they have expected text. If the checks pass, the test passes. The browser simulator closes after the test to keep things clean. This process helps test the app like a real user would, ensuring the interface works correctly.

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