Email previews in Ruby on Rails - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

How does Rails email preview render the email?

In Rails, when you open an email preview in the browser, what does Rails do to show the email content?

A It calls the mailer method and renders the email body as HTML or text in the browser.

B It sends the email to the configured SMTP server and shows the server response.

C It generates a PDF of the email and displays it in the browser.

D It only shows the email subject line without rendering the body.

💡 Hint

Think about how you can see the full email content without sending it.

Rails email previews call the mailer method and render the email body directly in the browser. This lets you see the email as it would appear to the user without actually sending it.

📝 Syntax

intermediate

Correct syntax to define a preview class for UserMailer

Which of the following is the correct way to define a preview class for a mailer named UserMailer in Rails?

A

class UserMailerPreview < ActionMailer::Preview
  def welcome_email
    UserMailer.welcome_email(User.first)
  end
end

B

class UserMailerPreview
  def welcome_email
    UserMailer.welcome_email(User.first)
  end
end

C

class UserMailerPreview < ApplicationMailer
  def welcome_email
    UserMailer.welcome_email(User.first)
  end
end

D

class UserMailerPreview < ActionController::Base
  def welcome_email
    UserMailer.welcome_email(User.first)
  end
end

💡 Hint

Preview classes inherit from a special Rails class for previews.

Preview classes must inherit from ActionMailer::Preview to work correctly in Rails.

❓ state_output

advanced

What is the output of this preview method?

Given this preview method in Rails, what will be the subject line shown in the preview if User.first has email '[e-mail]'? class UserMailerPreview < ActionMailer::Preview def notify UserMailer.notify(User.first) end end And the mailer method: class UserMailer < ApplicationMailer def notify(user) mail(to: user.email, subject: "Hello, #{user.email}") end end

A Hello, [e-mail]

B No subject line

C Hello, [e-mail]

D Hello,

💡 Hint

Look at how the subject is built using the user email.

The subject line uses string interpolation to include the user's email, so it will show "Hello, [e-mail]".

🔧 Debug

advanced

Why does this email preview raise an error?

This preview method raises an error when accessed: class UserMailerPreview < ActionMailer::Preview def alert UserMailer.alert(nil) end end Mailer method: class UserMailer < ApplicationMailer def alert(user) mail(to: user.email, subject: "Alert") end end What is the cause of the error?

A Preview class must inherit from ApplicationMailer.

B Calling user.email on nil causes a NoMethodError.

C Mailer method alert is not defined properly.

D The mail method requires a block to render the email.

💡 Hint

Check what happens when you call a method on nil.

Passing nil as user causes user.email to raise a NoMethodError because nil has no email method.

🧠 Conceptual

expert

Why use email previews in Rails development?

Which of the following best explains the main benefit of using email previews in Rails development?

A They generate email templates in multiple languages automatically.

B They automatically send test emails to all users to verify email delivery.

C They replace the need for writing mailer tests in the test suite.

D They let developers see the email content in the browser without sending actual emails, speeding up design and testing.

💡 Hint

Think about how previews help before sending emails.

Email previews allow developers to view and verify email content quickly in the browser without sending real emails, making design and testing faster and safer.