Essential Work Sample Exercises for Evaluating Junior Software Engineer Candidates

Junior software engineers form the foundation of technical teams, bringing fresh perspectives and energy while developing into the senior engineers of tomorrow. Finding the right junior talent is crucial for building a sustainable engineering organization, but evaluating candidates with limited professional experience presents unique challenges.

Traditional interviews often fail to reveal a candidate's true potential, especially for junior roles where academic credentials and theoretical knowledge may not translate to practical skills. Work samples provide a window into how candidates approach real-world problems, their coding style, attention to detail, and ability to learn—all critical indicators of future success.

The following exercises are designed to evaluate junior software engineers holistically, assessing not just technical abilities but also problem-solving approaches, communication skills, and coachability. By implementing these structured work samples, hiring teams can make more informed decisions based on demonstrated skills rather than resume keywords or interview performance alone.

These exercises simulate the actual work junior engineers will perform, creating a fair and relevant assessment environment. Additionally, they give candidates insight into your company's technical challenges and working style, helping them determine if the role is a good fit from their perspective as well.

Activity #1: Bug Fix Challenge

This exercise evaluates a candidate's debugging skills, attention to detail, and ability to understand existing code—essential skills for junior engineers who will often be tasked with maintaining and fixing code written by others.

Directions for the Company:

• Select a small, self-contained piece of code (50-100 lines) from your codebase that contains 2-3 deliberate bugs of varying difficulty.
• Remove any company-specific references or complex dependencies.
• Provide the candidate with the buggy code, a description of what the code should do when working correctly, and any error messages or unexpected behaviors currently occurring.
• Allow 45-60 minutes for this exercise.
• Prepare a development environment where the candidate can run and test the code (either a simplified local setup or an online IDE like CodeSandbox or Replit).

Directions for the Candidate:

• Review the provided code and understand its intended functionality.
• Identify and fix the bugs in the code.
• Document each bug you find, explaining what was causing the issue and how you fixed it.
• If time permits, suggest any improvements to the code structure or readability.
• Be prepared to explain your debugging process and reasoning behind your fixes.

Feedback Mechanism:

• After the candidate completes the exercise, provide feedback on one aspect they handled well (e.g., "You quickly identified the null reference issue in the data processing function") and one area for improvement (e.g., "Consider how error handling could be more robust").
• Give the candidate 10-15 minutes to implement the improvement suggestion and explain their approach to addressing the feedback.

Activity #2: Pair Programming Session

This collaborative exercise assesses how candidates think through problems in real-time, communicate technical concepts, and respond to guidance—crucial skills for junior engineers who will work closely with more experienced team members.

Directions for the Company:

• Prepare a small, well-defined programming task that can be completed in 30-45 minutes (e.g., implementing a specific algorithm or building a simple feature).
• Choose a task that's representative of your actual work but doesn't require deep domain knowledge.
• Assign an experienced engineer to pair with the candidate.
• Set up a shared coding environment (like VS Code Live Share, CodeSandbox, or screen sharing with a collaborative editor).
• Brief the paired engineer to act as a collaborative partner, not an interrogator, offering guidance when needed but allowing the candidate to lead.

Directions for the Candidate:

• You'll be working with one of our engineers to solve a programming problem together.
• Take the lead in thinking through the problem and writing code.
• Verbalize your thought process as you work.
• Feel free to ask questions and discuss approaches with your pair.
• The goal is not just to complete the task but to demonstrate how you collaborate and solve problems.

Feedback Mechanism:

• Halfway through the session, the paired engineer should provide one piece of positive feedback and one suggestion for improvement.
• The candidate should incorporate the feedback for the remainder of the session.
• At the end, discuss what went well and what could have been approached differently.

Activity #3: Code Review Exercise

This exercise evaluates a candidate's ability to read and understand code written by others, identify issues, and communicate feedback constructively—skills that are essential for contributing to team code quality.

Directions for the Company:

• Select a code snippet (100-200 lines) that contains various issues: bugs, performance problems, security vulnerabilities, and style inconsistencies.
• Include some good practices as well, so it's not just about finding flaws.
• Provide context about what the code is supposed to do and any relevant coding standards your team follows.
• Allow 45-60 minutes for the review.
• Prepare a document or tool where the candidate can leave their comments.

Directions for the Candidate:

• Review the provided code as if you were doing a code review for a team member.
• Identify and document any issues you find, categorizing them as:
• Functional bugs
• Performance concerns
• Security vulnerabilities
• Style/readability issues
• Potential improvements
• For each issue, explain why it's a problem and suggest a solution.
• Be constructive and specific in your feedback.
• Highlight any positive aspects of the code as well.

Feedback Mechanism:

• After reviewing the candidate's comments, provide feedback on the thoroughness of their review and the quality of their suggestions.
• Point out one type of issue they missed or could have addressed more effectively.
• Ask the candidate to revise or expand on their feedback for that specific issue, demonstrating how they would incorporate your guidance.

Activity #4: System Design and Planning

This exercise assesses a candidate's ability to think about software architecture, plan their work, and communicate technical concepts—skills that differentiate promising junior engineers who can grow into more senior roles.

Directions for the Company:

• Create a scenario for a small feature or component that requires some design decisions (e.g., "Design a user profile management system" or "Create a caching mechanism for frequently accessed data").
• The scenario should be complex enough to have multiple valid approaches but simple enough for a junior engineer to tackle in 45-60 minutes.
• Provide any constraints or requirements that would influence the design (e.g., performance needs, scalability concerns, or integration with existing systems).
• Prepare a whiteboard (physical or digital) or diagramming tool for the candidate to use.

Directions for the Candidate:

• Read the provided scenario and requirements carefully.
• Create a high-level design for the described feature or component.
• Your design should include:
• A diagram showing the main components and their interactions
• Data structures or models you would use
• Key functions or methods you would implement
• Any important algorithms or patterns you would apply
• Be prepared to explain your design choices and discuss alternatives you considered.
• Focus on clarity and communication—we're interested in your thinking process as much as the final design.

Feedback Mechanism:

• After the candidate presents their design, provide feedback on one strong aspect of their approach and one area where their design could be improved or might face challenges.
• Ask the candidate to revise part of their design based on your feedback, explaining how they would address the concern you raised.
• Observe how they incorporate feedback and whether they can adapt their thinking.

Frequently Asked Questions

How long should each work sample take?

Each exercise is designed to take 45-60 minutes. For a comprehensive assessment, you might spread these across multiple interview stages rather than conducting all four in a single session. For example, the Bug Fix Challenge could be a take-home exercise, while the Pair Programming Session would be part of an on-site interview.

Should we use our actual codebase for these exercises?

While using simplified versions of your actual code provides the most relevant assessment, ensure you're not exposing proprietary information. Sanitize the code by removing business logic and replacing domain-specific terms. Alternatively, create exercises that mirror your typical challenges without using actual code.

What if a candidate doesn't complete the exercise in the allotted time?

Focus on the quality of what they did complete rather than completion alone. Junior engineers often underestimate task complexity. Observe how they prioritize their time and whether they communicate proactively about challenges. The ability to recognize and articulate limitations is valuable.

How should we evaluate candidates who use different approaches than we expected?

Different approaches often reveal unique strengths. Evaluate whether their solution is effective and maintainable, not whether it matches your expected approach. This diversity of thinking can be valuable to your team. However, if they ignore explicit requirements or constraints, that may indicate issues with attention to detail or comprehension.

What accommodations should we make for candidates with different backgrounds?

Candidates from non-traditional backgrounds may be unfamiliar with certain industry practices but excel in problem-solving. Consider providing a brief primer on any tools or practices you expect them to use. Judge them on learning ability and fundamental skills rather than familiarity with specific technologies they can learn on the job.

How do we ensure these exercises don't disadvantage candidates from underrepresented groups?

Review exercises for assumptions about background knowledge that might create artificial barriers. Provide clear instructions and evaluation criteria. Consider having diverse team members review the exercises for potential bias. Focus evaluation on demonstrated skills rather than cultural fit or communication style preferences.

These work samples provide a comprehensive view of a junior software engineer's capabilities, helping you identify candidates with the technical skills, problem-solving abilities, and growth potential needed to succeed in your organization. By implementing structured, relevant exercises with clear feedback mechanisms, you'll make more informed hiring decisions while giving candidates valuable insight into your company's work environment.

For more resources to improve your hiring process, check out Yardstick's AI Job Description Generator, AI Interview Question Generator, and AI Interview Guide Generator.

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