How Do You Test a Developer's Problem-Solving Skills?

Finding a developer who can actually solve problems rather than just write code is surprisingly difficult. I mean, you can have someone with perfect syntax and a beautiful portfolio, but the moment they hit a real-world issue that doesn't have a Stack Overflow answer, they completely freeze up. I've seen this happen more times than I'd like to admit—and its not just junior developers either. Some people with years on their CV still cant think their way through unexpected challenges, and that's exactly what mobile app development throws at you daily.

The thing is, building apps for healthcare companies or fintech clients isn't like following a tutorial. You get weird edge cases, API failures, device-specific bugs that only happen on certain Android phones... basically, things break in ways you never anticipated. And when they do, you need someone who can actually work through the problem methodically rather than panic or start randomly changing code hoping something works. That's why I've spent years refining how we test for problem-solving skills before bringing developers onto projects; it saves an enormous amount of time and frustration later.

The best developers dont just fix bugs—they understand why the bug happened in the first place and how to prevent similar issues down the line

What makes testing these skills tricky is that its not about memorising algorithms or knowing every framework. Sure, technical knowledge matters, but problem-solving is more about approach, thinking patterns, and how someone handles uncertainty. Throughout this guide, I'll walk you through the exact methods I use to evaluate developers—from practical coding challenges to reviewing their past work, spotting red flags, and understanding what good problem-solving actually looks like in mobile development. These aren't theoretical exercises either; they're based on real situations that have helped us build successful apps across different industries.

Understanding What Problem-Solving Really Means for Developers

When I'm hiring developers for our agency, I've learned that problem-solving isn't really about memorising algorithms or reciting design patterns—its about how someone thinks when they hit a wall. The best developers I've worked with don't panic when something breaks; they get curious. They ask questions. They break the problem down into smaller chunks until they find the bit that's causing trouble.

I remember working on a fintech app where transactions were randomly failing for about 3% of users. No error logs, no pattern we could spot. A junior developer would've probably just tried random fixes or blamed the backend team, but our lead developer spent two days methodically testing every edge case until he found it—turns out users with certain special characters in their names were breaking the API call. That's proper problem-solving: patient, systematic, and driven by data rather than guesswork.

Here's what I actually look for when testing problem-solving skills:

• Can they explain their thinking process out loud as they work through a challenge?
• Do they ask clarifying questions before diving into code?
• How do they handle getting stuck—do they freeze up or try a different approach?
• Can they identify what information they need to solve a problem?
• Do they consider multiple solutions before settling on one?

Technical Skills vs Problem-Solving Ability

You know what? I've seen developers with impressive CVs completely freeze when faced with a real-world problem that doesn't match a textbook example. Meanwhile, I've hired self-taught developers who might not know every framework but can figure their way through any challenge you throw at them. The difference is huge. Technical skills and technology choices can be taught in a few months, but that instinct for breaking down complex problems and finding elegant solutions—thats much harder to develop.

Setting Up Practical Coding Challenges

The coding challenges you set up need to mirror the actual work your developer will be doing, not some abstract algorithm they'll never use. I've seen too many companies waste time with generic whiteboard exercises that test nothing except how well someone can recall computer science theory under pressure. When I'm hiring developers for app projects, I give them problems we've actually faced—like building a pull-to-refresh mechanism that feels responsive even on slower connections, or handling offline data sync for a healthcare app where patient records can't just disappear if the wifi drops.

The best format I've found is a take-home challenge that takes about 2-3 hours. Any longer and you're disrespecting their time; any shorter and you wont get a real sense of their abilities. I usually provide a simplified version of something we've built before—maybe a feed screen with infinite scroll, or a form with proper validation that needs to work across different device sizes. The key is giving them enough context that they understand the business requirements, not just the technical specs.

Here's what I look for when setting up these challenges:

• Clear requirements but room for interpretation—you want to see how they make decisions when things aren't perfectly specified
• At least one performance consideration—can they spot where things might get slow with larger datasets?
• Some aspect of user experience—do they think about loading states, error handling, accessibility?
• Code organisation—how do they structure files and separate concerns?

One thing that's worked really well for us is including a small bug in the starter code. Nothing obvious, but something that'll cause issues if they don't read through what they're given. I once worked on a fintech app where a rounding error in currency calculations wasn't caught until late in testing because nobody questioned the existing code. That cost us two weeks of delays. Developers who spot these issues before they start coding? That's the attention to detail you need.

Don't make candidates build everything from scratch—give them a realistic starting point with some existing code they need to work with or modify. Real development is rarely greenfield, and you need to see how they navigate codebases they didn't write.

Structuring the Challenge Instructions

Your instructions matter more than you'd think. I keep mine conversational but specific—explain what the feature should do from a user perspective first, then list any technical constraints. For example, "Users need to filter their transaction history by date range and category. The API returns up to 1000 transactions at once, and some users have accounts going back five years." That tells them there's a potential performance issue without spelling it out. If they come back with a solution that tries to load everything into memory at once, that's a red flag. If they ask questions about pagination or suggest implementing virtual scrolling? They're thinking ahead.

Providing the Right Development Environment

Make it easy for them to get started. I usually provide a basic project setup with dependencies already configured—you're testing their coding skills, not their ability to configure webpack or gradle. For mobile developers specifically, I'll specify which minimum iOS or Android version to target and whether they should use any particular libraries we commonly use. But I also leave room for them to suggest alternatives if they have good reasons. Actually, some of our best hires have been developers who came back and said "I noticed you're using X for state management, but for this specific use case Y might be more appropriate because..." That shows independent thinking.

Evaluating Their Approach to Debugging

I've interviewed hundreds of developers over the years and honestly, watching someone debug is like seeing their brain work in real-time. You learn more in fifteen minutes of debugging than you would from an hour of technical questions. When I'm assessing a developer's problem-solving skills, I don't just want to see if they can fix a bug—I want to understand how they think when things go wrong, because lets face it, things go wrong constantly in mobile development.

Here's what I do: I give them a small piece of code with a deliberate bug in it. Nothing too obscure, but not immediately obvious either. Maybe its a React Native component that crashes when users scroll too quickly, or an API call that fails intermittently. The actual bug doesn't matter as much as watching their process. Do they immediately start changing random things hoping something will work? That's a red flag. Or do they methodically work through the problem, checking logs, adding breakpoints, isolating variables? That's what I'm looking for.

The best developers I've worked with all share this trait—they ask questions before they start fixing. "What device was this tested on?" "When did the bug first appear?" "Can we reproduce it consistently?" These questions show they understand that debugging isn't about guessing, its about eliminating possibilities until you find the root cause. I remember working on a fintech app where transactions would occasionally fail without any error message. A junior developer wanted to just add more error handling. A senior developer I brought in spent twenty minutes asking questions about our backend architecture and network timeout settings before even opening the code... and found the issue in five minutes after that.

You also want to see if they can explain their thinking as they go. Can they articulate why they're checking the console logs first? Can they explain what they expect to see versus what they're actually seeing? This matters because mobile development is collaborative work—if they cant communicate their debugging process to you during an interview, they definitely wont be able to explain it to your project manager or client when a critical bug appears in production.

Using Real-World Scenarios in Your Assessment

Here's what I do when testing developers—I give them problems from actual projects we've faced. Not made-up textbook exercises, but real scenarios that caused us genuine headaches. For example, I might describe a situation where a fintech app's transaction list was taking 8 seconds to load because the previous developer was making separate API calls for each transaction instead of batching them. Then I ask how they'd approach fixing it. The answers tell me everything I need to know about their problem-solving process.

The best candidates don't just jump straight to "use pagination" or "implement caching"—they ask questions first. What's the data structure? How many transactions are typical users viewing? Are there network constraints we need to consider? This questioning phase is absolutely critical because it shows they understand that real problems rarely have simple, one-size-fits-all solutions. I've hired developers who gave technically correct answers but never asked about the business context, and honestly, they struggled when faced with actual client projects where requirements weren't perfectly defined.

Real-world scenarios reveal whether a developer can navigate ambiguity and balance technical constraints with business needs, which is what you'll need them to do every single day

Another scenario I use involves push notifications—specifically, a healthcare app where we needed to send medication reminders without draining the battery or annoying users into disabling notifications entirely. There's no "right" answer here; its about watching how they weigh different factors like user experience, technical limitations, and compliance requirements. The developers who've actually built consumer apps will immediately think about notification frequency, timing preferences, and fallback strategies. Those who haven't? They'll focus purely on the technical implementation without considering why half the users might just turn notifications off completely.

Testing Communication and Collaboration Skills

Here's something I've learned the hard way—a developer who can solve complex problems but can't explain their thinking is only half as valuable as one who can do both. I mean, you could have the most elegant solution in the world, but if you cant walk your team through it or collaborate on refinements, that code is going to cause problems down the line. When I'm assessing developers, I actually care about their communication skills almost as much as their technical abilities, because apps aren't built in isolation; they're built by teams who need to understand each other.

The way I test this is pretty straightforward but revealing. During the coding challenge or debugging session, I'll interrupt them mid-flow and ask them to explain what they're doing and why they chose that approach. Not in a gotcha way—just genuinely asking them to walk me through their thought process. The good ones? They can articulate their reasoning clearly, maybe even sketch out the architecture or use simple terms to explain complex logic. The ones who struggle to communicate will often get defensive or frustrated, or they'll use so much jargon that its clear they're hiding behind complexity rather than clarifying it. This is where explaining technical concepts to non-technical stakeholders becomes crucial.

How They Handle Feedback Matters

I also pay attention to how they respond when I suggest a different approach or point out a potential issue with their solution. Do they get defensive and dig in? Or do they listen, consider the feedback, and either explain why their way works better or adapt their thinking? On a fintech project we built for a payment processing platform, we had a developer who was technically brilliant but absolutely refused to consider alternative solutions once he'd settled on an approach. It created friction with the rest of the team and slowed down development because every decision became a debate rather than a discussion.

Team Dynamics in Practice

If possible, I try to include a collaborative element in the assessment itself—maybe pair them with another developer on your team for part of the challenge, or have them review someone else's code and provide feedback. You learn so much about someone when you see how they interact with peers. Are they respectful? Do they ask clarifying questions before making assumptions? Can they give constructive criticism without being condescending? These soft skills determine whether someone will lift your team up or drag it down, regardless of how many algorithms they've memorised. Understanding how developers collaborate is essential for building successful teams.

Reviewing Past Projects and Code Samples

Looking at a developer's previous work tells you more about their problem-solving abilities than any interview question ever could. I mean, you're literally seeing how they approached real challenges and solved actual problems. When I'm evaluating a developer, I always ask for their GitHub profile or a portfolio of projects they've worked on—and I spend proper time digging through their code, not just skimming the surface.

The first thing I check is how they structure their code; good problem solvers write code that other developers can actually understand months later. I look for clear variable names, sensible file organisation, and comments that explain the why behind complex logic (not just what the code does, which is obvious). Its about whether they were thinking about the next person who'd need to work on this. And here's something interesting—I've noticed that developers who've solved difficult problems before tend to leave breadcrumbs in their code... little notes about edge cases they handled or why they chose one approach over another.

I also look at their commit history because it shows their thinking process. Do they make tiny, incremental changes or massive commits that change hundreds of files at once? Developers who break problems down into smaller pieces usually have stronger problem-solving skills. They can see the big picture but tackle it step by step. When reviewing their projects, I'll often ask them to walk me through a specific challenge they faced—maybe it was handling offline data sync in a mobile app or optimising image loading for slower connections. How they explain their thought process and the trade-offs they considered? That's gold. This is particularly important when considering how developers manage app maintenance and updates.

Ask developers to share both their proudest project and one they'd approach differently now. Their ability to critique their own past work shows growth and self-awareness—two traits that make exceptional problem solvers.

What to Look for in Their Code Quality

Quality isn't just about code that works, it's about code that keeps working when requirements change. When I'm reviewing samples, I check whether they've written tests—unit tests, integration tests, anything that shows they think about how their code might break. Developers who write tests are naturally better problem solvers because they've already considered all the ways things could go wrong before they happen. I've worked with plenty of talented developers over the years, and the ones who last in this industry are those who build in safety nets.

Understanding Their Problem-Solving Evolution

One thing that really stands out is seeing how a developer's work has evolved over time. If you can look at projects from different periods—say something they built two years ago versus something recent—you can see how they've grown. Better problem solvers constantly refine their approach; they learn from mistakes and apply those lessons to future work. I actually prefer seeing a mix of polished work and some rough edges because it shows they're comfortable sharing their learning journey rather than just showcasing their greatest hits. Understanding how they approach breaking down complex projects reveals their strategic thinking abilities.

Red Flags to Watch Out For During Testing

I've interviewed hundreds of developers over the years and there are certain warning signs that pop up again and again. The biggest one? When a candidate blames everyone else for problems in their past projects. I mean, sure, sometimes you get difficult clients or legacy code that's a nightmare to work with—but developers who can't take any ownership for past failures usually become problems themselves. I once hired someone who spent the entire technical interview explaining why his previous team was incompetent; three months later he was doing the same about our codebase, and it wasn't pretty.

Another red flag is when developers can't explain their code in simple terms. If someone built a payment integration for a fintech app but cant walk you through why they chose a particular approach without getting lost in jargon, that's trouble. The best developers I've worked with can explain complex things simply because they genuinely understand what theyre doing. Its not about dumbing things down—it's about clarity of thought. This becomes especially important when dealing with payment processing systems where clear understanding is crucial.

Watch How They Handle Uncertainty

Here's what really separates good developers from problematic ones: how they react when they don't know something. If a candidate pretends to know every framework, every design pattern, every solution... run. The mobile landscape changes constantly and nobody knows everything. I'd much rather hire someone who says "I haven't used that particular library but here's how I'd approach learning it" than someone who bullshits their way through every question.

The Copy-Paste Developer

You can usually spot copy-paste developers during code reviews. They'll have solutions that work but they cant explain why certain lines are there or what specific methods actually do. I had a developer once submit a React Native component that handled push notifications perfectly... but when I asked him to modify the behaviour slightly, he was completely lost. Turns out he'd copied the entire thing from Stack Overflow without understanding any of it. Look for developers who can adapt and modify their code, not just implement it once and hope it works.

Conclusion

Testing a developer's problem-solving skills isn't a one-time checkbox exercise—its an ongoing evaluation that starts in the interview and continues throughout the project. After hiring dozens of developers over the years for everything from healthcare apps with complex HIPAA requirements to fintech platforms handling millions in transactions, I've learned that the best assessment combines multiple approaches. You need the practical coding challenges to see their technical chops, sure, but you also need those real-world scenarios to understand how they think under pressure and those communication tests to see if they can actually explain their decisions to non-technical stakeholders.

The biggest mistake I see companies make? They focus too heavily on algorithmic puzzles and not enough on the messy, real problems that come up in actual app development. When your production app crashes because of a memory leak on older Android devices, you don't need someone who can reverse a binary tree—you need someone who can methodically track down the issue, communicate progress to anxious clients, and implement a fix that doesn't break something else. That's the kind of problem-solving that matters.

Look, finding the right developer takes time and effort. There's no magic question or test that'll instantly reveal whether someone's brilliant or rubbish. But if you combine practical assessments with careful observation of how they approach problems, ask questions, and communicate their thinking, you'll spot the developers who can genuinely move your project forward. Trust your gut when you see those red flags we discussed, but also give candidates the chance to show you how they actually work. The developers who've built the best apps for my clients over the years weren't necessarily the ones who aced every technical question—they were the ones who asked the right questions, admitted what they didn't know, and showed genuine curiosity about solving the real business problem behind the app.