Gemfile and dependency management in Ruby on Rails - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What happens when you run bundle install with a Gemfile.lock present?

You have a Gemfile and a Gemfile.lock in your Rails project. You run bundle install. What does Bundler do?

A It ignores <code>Gemfile.lock</code> and installs the latest versions allowed by <code>Gemfile</code>.

B It deletes <code>Gemfile.lock</code> and installs gems fresh from the internet.

C It installs the exact gem versions listed in <code>Gemfile.lock</code>, ignoring version changes in <code>Gemfile</code>.

D It only updates gems that are missing, leaving others untouched regardless of <code>Gemfile</code>.

💡 Hint

Think about how Bundler ensures consistent gem versions across machines.

Bundler uses Gemfile.lock to lock gem versions. When present, bundle install installs exactly those versions to keep consistency.

📝 Syntax

intermediate

Which Gemfile syntax correctly specifies a gem only for the development environment?

You want to add the gem pry only for development. Which Gemfile snippet is correct?

A

group :dev do
  gem 'pry'
end

B gem 'pry', group: :development

C gem 'pry', only: :development

D

group :development do
  gem 'pry'
end

💡 Hint

Remember the standard way to group gems by environment in Bundler.

The group :development do ... end syntax is the correct way to specify gems for a specific environment. Option D is invalid syntax, C uses a wrong key, and D uses a non-existent group name.

🔧 Debug

advanced

Why does bundle exec rails server fail with 'Could not find gem' error after adding a new gem?

You added a new gem to your Gemfile and ran bundle install. But running bundle exec rails server gives an error: 'Could not find gem ...'. What is the likely cause?

A You did not run <code>bundle install</code> after adding the gem to Gemfile.

B You added the gem but did not run <code>bundle update</code> to update Gemfile.lock.

C You forgot to restart your terminal or shell session after installing the gem.

D You installed the gem globally instead of using Bundler.

💡 Hint

Think about how Bundler uses Gemfile.lock to track installed gems.

After adding a gem, running bundle install updates Gemfile.lock only if the gem version is new or missing. Sometimes you need bundle update to update Gemfile.lock and resolve dependencies properly.

🧠 Conceptual

advanced

What is the purpose of the source line in a Gemfile?

In a Gemfile, you often see a line like source 'https://rubygems.org'. What does this line do?

A It sets the environment variable for gem installation.

B It tells Bundler where to fetch gems from when installing dependencies.

C It defines the local path where gems are stored on your machine.

D It specifies the Ruby version to use for the project.

💡 Hint

Think about where gems come from when you run bundle install.

The source line tells Bundler the URL of the gem server to download gems from, usually https://rubygems.org.

❓ state_output

expert

What is the content of Gemfile.lock after running bundle install with this Gemfile?

Given this Gemfile:

source 'https://rubygems.org'
gem 'rails', '~> 7.0.0'
group :development do
  gem 'pry'
end

You run bundle install on a fresh project. What will Gemfile.lock contain regarding the pry gem?

Ruby on Rails

source 'https://rubygems.org'
gem 'rails', '~> 7.0.0'
group :development do
  gem 'pry'
end

A <p><code>pry</code> and its dependencies are listed under the <code>development</code> group section in <code>Gemfile.lock</code>.</p>

B <p><code>pry</code> is listed under the <code>default</code> group in <code>Gemfile.lock</code>.</p>

C <p><code>pry</code> is not listed anywhere in <code>Gemfile.lock</code> because it's only for development.</p>

D <p><code>pry</code> is listed but without any group information in <code>Gemfile.lock</code>.</p>

💡 Hint

Consider how Bundler groups gems in the lockfile.

Bundler records gems in Gemfile.lock under their respective groups. Gems in group :development appear under the development group section.