Debugging with pry and byebug in Ruby - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output when using pry to inspect a variable?

Consider the following Ruby code snippet using pry. What will be printed when the program hits the binding.pry line and you type x in the pry console?

Ruby

require 'pry'
x = 10
binding.pry
puts "Done"

A 10

B nil

C Error: undefined local variable or method `x`

D Nothing is printed

💡 Hint

Remember that binding.pry pauses execution and lets you inspect variables in the current scope.

When the program pauses at binding.pry, you can type x to see its value, which is 10.

❓ Predict Output

intermediate

What happens when byebug hits a breakpoint?

Given this Ruby code using byebug, what will be the output when the program pauses at byebug and you type y + 5 in the debugger console?

Ruby

require 'byebug'
y = 7
byebug
puts y + 3

A 10

B 12

C Error: undefined local variable or method `y`

D Nothing, program continues without pause

💡 Hint

Byebug pauses execution and lets you evaluate expressions in the current context.

At the byebug line, the program pauses. Typing y + 5 evaluates to 12 because y is 7.

❓ Predict Output

advanced

What error does this code raise when using pry incorrectly?

What error will this Ruby code raise when run?

Ruby

require 'pry'
Pry.start
x = 5

A No error, program runs fine

B RuntimeError: Pry session already started

C NoMethodError: undefined method `start` for Pry:Module

D SyntaxError: unexpected end-of-input

💡 Hint

Check if Pry.start is a valid method call.

Pry.start is not a defined method. The correct way to start a pry session is binding.pry.

❓ Predict Output

advanced

What is the output after continuing from a byebug breakpoint?

Given this Ruby code, what will be printed after you type continue in the byebug console?

Ruby

require 'byebug'
x = 3
byebug
x += 4
puts x

A 7

B Nothing, program stuck at breakpoint

C Error: undefined local variable or method `x`

D 3

💡 Hint

After continuing, the program runs the next lines normally.

After continue, x becomes 7 and is printed.

🧠 Conceptual

expert

Which option correctly explains the difference between pry and byebug?

Choose the best explanation of how pry and byebug differ in Ruby debugging.

A Pry only works with Rails apps; byebug only works with Ruby scripts.

B Pry and byebug are identical tools with different names.

C Pry is used for performance profiling; byebug is used for syntax checking.

D Pry is an interactive REPL allowing live code inspection and modification; byebug is a step-by-step debugger focused on breakpoints and stepping through code.

💡 Hint

Think about how each tool lets you interact with running code.

Pry provides a powerful interactive shell to inspect and modify code live. Byebug is designed for setting breakpoints and stepping through code execution.

Practice

1. What is the main purpose of using binding.pry or byebug in Ruby code?

easy

A. To pause the program and inspect variables at a specific point

B. To speed up the execution of the program

C. To automatically fix syntax errors

D. To compile Ruby code into machine code

Solution

1. Step 1: Understand the role of debugging tools

   Both binding.pry and byebug are used to pause program execution.

2. Step 2: Inspect variables and program state

   When paused, you can check variable values and program flow to find issues.

3. Final Answer:

   To pause the program and inspect variables at a specific point -> Option A

4. Quick Check:

   Debugging tools pause and inspect = A [OK]

Hint: They pause code to check variables and flow [OK]

Common Mistakes:

• Thinking they speed up code
• Believing they fix errors automatically
• Confusing with code compilation

2. Which of the following is the correct way to insert a breakpoint using Pry in Ruby code?

easy

A. debug.pry

B. breakpoint.pry

C. pry.binding

D. binding.pry

Solution

1. Step 1: Recall Pry syntax for breakpoints

   The correct syntax to pause execution with Pry is binding.pry.

2. Step 2: Check other options for correctness

   Other options like breakpoint.pry, pry.binding, and debug.pry are invalid method calls.

3. Final Answer:

   binding.pry -> Option D

4. Quick Check:

   Correct Pry breakpoint syntax = D [OK]

Hint: Use exactly 'binding.pry' to pause with Pry [OK]

Common Mistakes:

• Swapping method and object order
• Using non-existent methods
• Forgetting to require 'pry'

3. What will be the output when running this Ruby code with byebug inserted?

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

puts add(2, 3)

medium

A. 5

B. byebug error

C. nil

D. SyntaxError

Solution

1. Step 1: Understand what byebug does

   It pauses execution allowing inspection but does not change the return value.

2. Step 2: Trace the function call and output

   The method add(2, 3) returns 5, which is printed by puts.

3. Final Answer:

   5 -> Option A

4. Quick Check:

   byebug pauses but output is 5 [OK]

Hint: byebug pauses but returns normal output [OK]

Common Mistakes:

• Expecting byebug to change output
• Thinking byebug causes errors
• Confusing pause with program stop

4. You inserted binding.pry in your Ruby code, but when you run it, the program does not pause. What is the most likely reason?

medium

A. You used byebug instead of binding.pry

B. You forgot to require the 'pry' gem in your code

C. The Ruby version does not support debugging

D. You placed binding.pry after the return statement

Solution

1. Step 1: Check if 'pry' gem is loaded

   Without require 'pry', binding.pry is undefined and won't pause.

2. Step 2: Verify placement and usage

   Using binding.pry correctly requires the gem loaded; placing after return stops execution before breakpoint.

3. Final Answer:

   You forgot to require the 'pry' gem in your code -> Option B

4. Quick Check:

   Missing require 'pry' stops pause [OK]

Hint: Always require 'pry' before using binding.pry [OK]

Common Mistakes:

• Not requiring the gem
• Placing breakpoint after return
• Confusing pry with byebug usage

5. You want to debug a method that processes a list of numbers and stops only when a number is negative. Which debugging tool and approach is best to use?

hard

A. Use puts statements to print all numbers

B. Insert byebug at the start of the method without any condition

C. Insert binding.pry inside the loop with a condition to pause only if the number is negative

D. Run the program without breakpoints and guess the error

Solution

1. Step 1: Understand conditional breakpoints

   Using binding.pry with a condition lets you pause only when needed, saving time.

2. Step 2: Compare other options

   Using byebug without condition pauses every time, puts is less interactive, guessing is ineffective.

3. Final Answer:

   Insert binding.pry inside the loop with a condition to pause only if the number is negative -> Option C

4. Quick Check:

   Conditional breakpoint with binding.pry = A [OK]

Hint: Use conditional binding.pry to pause only on negative numbers [OK]

Common Mistakes:

• Pausing unconditionally causing many stops
• Relying only on print statements
• Ignoring debugging tools