As an application testing expert with over 10 years of hands-on experience validating software on thousands of real desktop and mobile devices, I’m thrilled to share my insider knowledge to unblur the lines between functional and non-functional testing.
In this epic yet easily digestible guide, we’ll journey together to unpack exactly how functional and non-functional testing differ, debunk common misconceptions, and empower you with actionable best practices to start improving testing in your organization today.
Defining Our Destination: What is Functional vs Non-Functional Testing?
Before diving deeper, it’s important to clearly define what we mean by functional vs non-functional testing at a high level…
Functional testing confirms that all declared and required behaviors for application features work per specifications without defects.
Using real user data, functional testing executes code and exercises interfaces to verify the accuracy of inputs, outputs, calculations and system interactions.
Non-functional testing evaluates more qualitative attributes of a system related to usability, performance efficiency, reliability or security.
Rather than checking business logic, non-functional testing observes behaviors under stressed conditions, models hacking attacks, measures resource usage or assesses how intuitive interfaces are for humans.
Navigating Key Differences
Now that we share an understanding of the core definitions, let’s map out key differences between these test types:
Functional Testing
- Tests specific application features and code capabilities
- Validates accuracy of computations, data manipulations and workflows
- Ensures adherence to requirements and business rules
- Performed early to guide development
- Both manual and automated testing
Non-Functional Testing
- Assesses broader quality attributes like site responsiveness
- Evaluates behaviors under heavy loads or duress
- Examines vulnerabilities, capacity limits and optimizations
- Conducted later to finalize product polish
- Often heavily automated testing
Simply put, functional testing provides the foundation to prove everything works as intended while non-functional testing supplies the ceiling exposing where the breaking points live.
Both lend superpowers allowing teams to deliver higher quality software aligned to specifications and resilient to variable real-world conditions…
Myriad Types to Unpack
Now what exactly constitutes a functional test case vs a non-functional one? Let’s expand on common types falling under each bucket…
Functional Testing Types
- Unit Testing – Validating individual code components and objects
- Integration Testing – Evaluating interactions between services, databases and APIs
- System Testing – Testing full application behavior
- Regression Testing – Re-running test cases after changes
- Acceptance Testing – Formal testing for users to deem ready
Non-Functional Testing Types
- Usability Testing – Testing ease of use and navigation
- Load Testing – Measuring performance under traffic spikes
- Security Testing – Checking vulnerabilities to attacks
- Localization Testing – Testing adaptations to country or language needs
Now let’s bring these types to life with illustrative examples…
Imagine ACME Tools launches an ecommerce site to sell power tools directly to consumers.
Functional Tests would:
- Check users can browse inventory, add items to cart, and complete checkout
- Validate promo codes apply correct percentage discounts
- Confirm order history pages show correct details
Non-Functional Tests would:
- Load test site with 10000 concurrent users to meet Black Friday demands
- Execute SQL injections to harden site against cyber threats
- Localize site for Spanish-speaking North American customers
Again, functional testing allows ACME to builds features correctly while non-functional testing helps them scale securely.
Charting Treacherous Testing Costs
Beyond the definitions and types of tests, what happens when functional or non-functional validation gets minimized or neglected entirely?
Let’s examine alarming statistics revealing the costs of inadequate testing:
| 56% of web/mobile applications fail quality standards | On average, software defects cost $25-$100 to fix early but $10,000 later |
| 63% of sites exceed 4+ second load times losing conversions | Cyber attacks often trace back to unaddressed software flaws |
| 65% of consumers will not return after just 1 negative experience | Worldwide cost of cybercrime damages projected to hit $10.5 trillion by 2025 |
Clearly robust functional and non-functional testing form crucial, non-negotiable foundations for releasing high quality software users love.
Next let‘s navigate options with testing tools…
Charting Our Course with Testing Tools
Thankfully a myriad of functional and non-functional testing tools exist to support validation efforts.
Let‘s compare the trade-offs of commercial vs open source tools available:
Commercial Testing Tools
- Pros: Superior support, advanced integrations, enhanced reporting
- Cons: Can be very costly, require lengthy procurement cycles
Examples:
- HPE LoadRunner for load testing
- SmartBear TestComplete for test automation
Open Source Testing Tools
- Pros: Completely free, customizable, transparent
- Cons: Typically less support, smaller feature set
Examples:
- Selenium for test automation
- JMeter for load testing
When to go Commercial?
- Heavy need for tech support or expert guidance
- Complex systems with many integrations
- Budget for total cost of ownership
When to use Open Source?
- Grassroots projects with limited funding
- Need for full customization of testing framework
- Technical skills to self-manage and troubleshoot
Expanding on commercial examples, tools like BrowserStack grant affordable access to perform both manual and automated cross browser testing on 3000+ real devices without any infrastructure costs.
Determining right-fit tools requires balancing technical needs, team skills, and budget. But combining open source and commercial solutions helps optimize thorough testing in a capital efficient manner.
Now that we‘ve aligned on helpful tools, what practices set testing heroes apart?
Navigating Best Practices
Over years of designing and executing test plans, I‘ve compiled tips any team can apply to amplify functional and non-functional testing powers:
Functional Testing Best Practices
- Expand test coverage for edge cases with techniques like boundary and decision table analysis
- Start unit testing new features before integration to detect defects early
- Rigorously verify computations, data validation rules and reporting functions
- Automate regression testing to lower maintenance costs over time
- Trace tests back to product requirements and user stories
Non-Functional Testing Best Practices
- Define quantitative site speed and uptime benchmarks to track optimizations
- Identify peak load capacity limits through incremental stress tests
- Budget time for page speed enhancements based on real user data
- Research and test for OWASP top 10 web application security risks
- Monitor production logs for errors revealing reliability gaps
Diverse perspectives also multiply testing superpowers…
I always engage product managers, developers, ops AND real users to help design functional and non-functional test cases reflective of how software gets built, deployed, and actually used in practice.
Aligning tests to satisfy the needs of all key stakeholders ensures everything important gets validated at the right time.
Recounting Battle Stories from the Testing Trenches
While we’ve covered high level functional vs non-functional differences, I wanted to briefly share a dramatic experience that etched deeply why non-functional testing CANNOT be shortchanged…
Many moons ago, I was working as a Performance Test Engineer for a large multi-national bank. They aimed to launch an updated mobile banking application right before the holiday season to expand account management functionality.
However, during initial soak tests simulating just 500 concurrent active users, we noticed database connection timeouts causing catastrophic system failures.
As you can imagine for a bank with millions of customers, maintaining near 100% uptime even during traffic surges was an absolute business necessity.
By incrementally load testing early, we averted disaster mere weeks before the planned launch. We swiftly uncovered architecture bottlenecks that required re-engineering to sustain performance demands.
While additional work was needed, this early non-functional testing investment optimizing speed and stability saved my client reputationally and financially in the long run.
Key Takeaway: Don‘t shortchange non-functional testing investments, my friends!
Charting Our Next Steps
We‘ve covered a spectrum of functional vs non-functional testing concepts. Before we part ways, I want to suggest a few key next steps to immediately improve your testing game:
Expand Functional Testing
- Audit traceability of tests back to product requirements
- Boost unit test coverage for new features
- Research test automation frameworks like Selenium
Evolve Non-Functional Testing
- Define load, site speed and uptime KPIs
- Continuously security test for emerging threats
- Investigate real user monitoring tools
Enable Cloud Testing
- Utilize cloud device labs for cross browser testing
- Shift testing left to find UX issues earlier
- Confirm responsiveness across OS versions
It‘s been a sincere privilege walking through functional vs non-functional testing keys with you today. I hope these battle-tested best practices illuminate new ways to channel quality and propel your next software launch to new heights.
Onward my friends – let the testing transformation begin!
