How to test backend developers' skills - coding tests, backend interview questions and more

Article summary

In this article, we explore effective strategies for evaluating backend engineers during the interview process. We emphasize the importance of assessing core backend competencies through technical screenings, coding challenges, and problem-solving interviews. Additionally, we highlight the need to evaluate a candidate's adaptability to new languages and frameworks, as well as their behavioral and cognitive skills, to ensure a comprehensive understanding of their capabilities.

What are the most important skills of a backend developer, and how to test them?

Are you hiring backend engineers? It doesn't really matter whether your stack consists of PHP, Java, Node.js or other technology. Every backend developer should have a certain type of logical thinking and programming attitude that ensures they will deliver clean, high quality code. Finding the right candidate means assessing their technical and cognitive skills, including their ability to problem-solve, adapt, and learn new languages and frameworks.

Below you will find the list of the most important skills every developer should be experienced in.

1. Core Technical Competencies

• Data Structures and Algorithms: A solid grasp of data structures (e.g., arrays, linked lists, trees) and algorithms (e.g., sorting, searching) is fundamental for backend development. Even if a developer is primarily experienced in Java, these foundational skills are transferable across languages, including PHP, and indicate a strong technical base.

• Database Design and Query Proficiency: Backend developers should possess a thorough understanding of relational databases and be adept at writing complex queries, designing efficient schemas, and managing data normalization. Familiarity with NoSQL databases, such as MongoDB, is also advantageous if relevant to your tech stack.

• API Design Skills: Experience in designing RESTful APIs or working with GraphQL, and understanding HTTP methods (e.g., GET, POST, PUT, DELETE), is crucial. Effective API design includes structuring endpoints, handling responses, managing authentication, and producing documentation.

• Security Principles: Proficiency in backend security best practices—such as data encryption, input validation, and effective authentication and authorization—is essential.

• Testing Mindset: Familiarity with unit testing, integration testing, and automated testing workflows is highly beneficial. Developers experienced with testing frameworks in one language (e.g., JUnit in Java) can apply similar testing practices in PHP with tools like PHPUnit.

2. Problem-Solving and Systems Thinking

• Analytical Problem-Solving: A capable backend developer should demonstrate the ability to deconstruct complex issues into smaller, manageable tasks. Evaluating their problem-solving approach can be revealing; consider presenting them with an architectural design or debugging scenario and asking them to walk through their thought process.

• Systems Thinking: Backend roles demand an understanding of how various parts of a system interact and the ability to foresee the impact of changes in one area on other components. Assessing their understanding of the software development lifecycle, deployment pipelines, and DevOps practices will help gauge their depth of systems thinking.

3. Assessing Adaptability to New Languages and Frameworks

• Conceptual Transferability: Even if a candidate's primary language is Java, principles such as object-oriented programming (OOP), error handling, and concurrency apply broadly and are transferable to other languages, including PHP. Questions or tasks around core OOP concepts—like inheritance, polymorphism, and encapsulation—can offer insight into their readiness to work with PHP or other languages.

• Prior Experience in Learning New Languages: Ask about past experiences with learning new languages or frameworks. Developers who have worked across multiple languages (e.g., Python, Ruby, C++) often adapt more easily to a new stack. Candidates who actively explore new technologies tend to learn more quickly and efficiently.

• Hands-On Language Adaptability Test: Provide a brief coding task or project in PHP to evaluate their adaptability. Observing how they navigate PHP syntax, libraries, and framework conventions can be invaluable in gauging their capacity to learn new languages practically.

• Resourcefulness and Independent Learning: Inquire about their typical approach to learning through documentation, online forums, and other resources when tackling new technologies. Candidates who can independently research solutions and troubleshoot issues generally demonstrate a readiness to learn new languages effectively.

4. Behavioral and Cognitive Assessments

• Curiosity and a Growth-Oriented Mindset: Seek candidates who exhibit a passion for continuous learning, curiosity about emerging technologies, and an openness to experimenting with new concepts and tools.

• Problem-Solving in Ambiguous Scenarios: Present scenarios where they have limited information or documentation to assess how they handle ambiguity and approach creative problem-solving.

• Interpersonal and Collaborative Skills: Backend roles often require close collaboration with other teams, such as frontend and DevOps. Strong communication skills and the ability to understand and integrate cross-functional requirements are vital for success in backend development. Consider assessing their approach to collaboration and problem-solving within a team setting.

5. Sample Evaluation Process

1. Technical Screening: Begin with a technical quiz or screening assessment that evaluates their core backend competencies.

2. Coding Challenge: Provide a coding exercise (preferably in PHP) to see how effectively they adapt to the language. Tasks that involve implementing a basic API, structuring an application component, or querying a database can offer insights into their language adaptability.

3. Problem-Solving Interview: Use open-ended questions that touch on system design, data flow, and scalability challenges. Encourage the candidate to explain their thought process.

4. Behavioral Interview: Explore their experiences in learning new languages and frameworks in previous roles. Ask about their approach to managing challenges and knowledge gaps.

5. Pair Programming Session: If possible, arrange a pair-programming session with an in-house PHP engineer to observe how they tackle real-world coding tasks and respond to feedback in an unfamiliar language.

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