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.