Rubocop for linting in Ruby - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of Rubocop when analyzing this Ruby code?

Given the following Ruby code, what output will Rubocop produce regarding style offenses?

Ruby

def greet(name)
  puts "Hello, #{name}"
end

greet("Alice")

A No offenses detected

B Style/MethodDefParentheses: Use parentheses when defining a method

C Lint/UselessAssignment: Useless assignment to variable 'name'

D Style/StringLiterals: Prefer single-quoted strings when you don't need string interpolation or special symbols.

💡 Hint

Look for string style offenses in the code.

Rubocop prefers single quotes for strings without interpolation. The string "Hello, #{name}" uses double quotes but includes interpolation, so it is correct. However, the argument to greet is a double-quoted string without interpolation, which triggers the Style/StringLiterals offense.

🧠 Conceptual

intermediate

Which Rubocop cop detects unused variables?

Which Rubocop cop is responsible for detecting variables that are assigned but never used in Ruby code?

A Lint/UselessAssignment

B Style/UnusedVariable

C Lint/UnusedMethodArgument

D Style/UnusedBlockArgument

💡 Hint

Think about the cop that warns about useless assignments.

The Lint/UselessAssignment cop detects variables that are assigned a value but never used later in the code.

🔧 Debug

advanced

Why does Rubocop raise an error on this code snippet?

Consider this Ruby code snippet. Rubocop raises an error. What is the cause?

Ruby

class Person
  def initialize(name)
    @name = name
  end

  def greet
    puts "Hello, #{name}"
  end
end

A Lint/UselessInstanceVariable because @name is never used

B NameError because 'name' is undefined in greet method

C NameError because @name is not accessible in greet method

D No offenses detected

💡 Hint

Check variable scope inside methods.

The instance variable @name is assigned in initialize, but the greet method tries to use name without the @ sign, which is undefined in that scope. Rubocop detects this as a NameError risk.

📝 Syntax

advanced

Which option causes a Rubocop syntax offense?

Which of the following Ruby code snippets will cause Rubocop to report a syntax offense?

A

def add(a, b)
  a + b
  end

B

def add a, b
  a + b
end

C

def add(a, b)
  return a + b
end

D

def add(a, b)
  a + b
end

💡 Hint

Look for indentation and end keyword placement.

Rubocop enforces consistent indentation. Option A has the end keyword indented incorrectly, causing a style offense.

🚀 Application

expert

How many style offenses will Rubocop detect in this code?

Analyze the following Ruby code. How many style offenses will Rubocop report?

Ruby

class Calculator
  def add(a,b)
    a + b
  end

  def subtract(a, b)
    a - b
  end

  def multiply(a, b)
    a * b
  end

  def divide(a, b)
    return nil if b == 0
    a / b
  end
end

A 1

B 3

C 2

D 4

💡 Hint

Check method parameter spacing and return usage.

Rubocop will report two offenses: one for missing space after comma in def add(a,b) and one for unnecessary return in divide method.

Practice

1.

What is the main purpose of using Rubocop in Ruby programming?

easy

A. To manage Ruby gem dependencies

B. To run Ruby programs faster

C. To check code style and find errors

D. To compile Ruby code into machine code

Solution

1. Step 1: Understand Rubocop's role

   Rubocop is a tool that checks Ruby code for style issues and errors.

2. Step 2: Compare options

   Only To check code style and find errors describes checking code style and errors, which matches Rubocop's purpose.

3. Final Answer:

   To check code style and find errors -> Option C

4. Quick Check:

   Rubocop = code style and error checker [OK]

Hint: Rubocop checks style and errors, not speed or compilation [OK]

Common Mistakes:

• Thinking Rubocop runs or compiles code
• Confusing Rubocop with dependency managers
• Assuming Rubocop improves runtime speed

2.

Which command correctly runs Rubocop on your Ruby project from the terminal?

easy

A. execute rubocop

B. ruby rubocop

C. run rubocop

D. rubocop

Solution

1. Step 1: Identify the correct command

   The standard command to run Rubocop is simply rubocop in the terminal.

2. Step 2: Eliminate incorrect options

   Options B, C, and D are not valid terminal commands for Rubocop.

3. Final Answer:

   rubocop -> Option D

4. Quick Check:

   Run Rubocop with 'rubocop' command [OK]

Hint: Just type 'rubocop' in terminal to run it [OK]

Common Mistakes:

• Adding 'ruby' before rubocop
• Using 'run' or 'execute' commands incorrectly
• Confusing Rubocop command with Ruby interpreter

3.

Given this Ruby code saved in example.rb:

def greet(name)
  puts "Hello, #{name}!"
end

greet("Alice")

You run rubocop example.rb and get a warning about missing a blank line after method definition. What will Rubocop suggest?

medium

A. Add a blank line after the end of the method

B. Remove the blank line before calling greet

C. Change puts to print

D. Rename the method to greeting

Solution

1. Step 1: Understand Rubocop's style rule

   Rubocop often requires a blank line after method definitions for readability.

2. Step 2: Identify the suggested fix

   The warning suggests adding a blank line after the end of greet method, before the next code.

3. Final Answer:

   Add a blank line after the end of the method -> Option A

4. Quick Check:

   Blank line after method end = Rubocop style [OK]

Hint: Rubocop likes blank lines after method ends [OK]

Common Mistakes:

• Ignoring blank line warnings
• Changing code logic instead of style
• Misunderstanding the warning message

4.

Look at this Ruby code snippet:

def add(a, b)
  a + b
end

puts add(2, 3)

When running rubocop, you get an error about missing parentheses in method call. How do you fix it?

medium

A. Remove parentheses from def add(a, b)

B. Add parentheses around arguments in puts add(2, 3)

C. Add parentheses around a + b inside method

D. Change method name to add_numbers

Solution

1. Step 1: Understand Rubocop's style on method calls

   Rubocop prefers explicit parentheses in method calls with arguments for clarity.

2. Step 2: Apply fix to method call

   The call puts add(2, 3) should have parentheses around add(2, 3) to avoid ambiguity.

3. Final Answer:

   Add parentheses around arguments in puts add(2, 3) -> Option B

4. Quick Check:

   Method calls with args need parentheses [OK]

Hint: Put parentheses around method call arguments [OK]

Common Mistakes:

• Removing parentheses from method definitions
• Adding parentheses inside expressions unnecessarily
• Ignoring Rubocop's parentheses style

5.

You want to configure Rubocop to ignore style warnings about line length in your project. Which file and setting should you modify?

hard

A. Add Metrics/LineLength: with Enabled: false in .rubocop.yml

B. Add LineLength: ignore in Gemfile

C. Set rubocop --ignore-line-length in terminal

D. Remove rubocop gem from Gemfile

Solution

1. Step 1: Identify Rubocop config file

   Rubocop uses .rubocop.yml file to configure rules.

2. Step 2: Disable line length check

   Inside .rubocop.yml, setting Metrics/LineLength: Enabled: false disables that check.

3. Final Answer:

   Add Metrics/LineLength: with Enabled: false in .rubocop.yml -> Option A

4. Quick Check:

   Disable rules in .rubocop.yml [OK]

Hint: Disable rules in .rubocop.yml config file [OK]

Common Mistakes:

• Trying to disable rules via Gemfile
• Using wrong command line flags
• Removing Rubocop gem instead of configuring