What Is Functional Testing - Overview and Examples

Ideally, functional testing begins early and occurs continuously as you build and update your product’s software. The sooner you can test your product’s features and their expected behavior, the easier it is to course-correct if something isn’t working correctly. This process is also referred to as “validating your requirements.”

During the requirement-gathering phase, development teams design functional tests to verify that the software’s spec and user stories function as intended when used.

Many teams adopt the practice of test-driven development (TDD)—where you create the functional test before writing the code to satisfy it. Instead of entirely developing the new functionality, you write the minimum code needed for the test to pass. This “test-first” approach gives developers clear guardrails and prevents defects from being baked into the software.

As the product nears its release date, functional testing ramps up through integration tests (testing different parts together) and end-to-end tests (testing entire workflows). Once all test cases pass, you can give the green light for launch.

However, the testing process continues even after going live. With each update or enhancement, regression tests are run against existing features to catch any unintended side effects. This safety net enables you to evolve your product without affecting the user experience.

Functional testing is crucial to assess your product’s quality. However, like all testing methodologies, it has its shortcomings. You should balance it with other testing practices for complete risk coverage.

Here are some of functional testing’s main pros and cons.

Pros

• User-centric approach: By simulating real user scenarios, functional testing ensures your software works properly from the customer’s point of view. It keeps you focused on what matters most—delivering a great user experience.

• Catches critical defects: Functional testing exposes bugs and issues that risk breaking your product’s core functionality before it reaches your end users. This prevents customer frustration and reputation-damaging problems.

• Systematically tests all paths: Comprehensive functional test suites systematically check and validate all possible user journeys, no matter how complex. This leaves no stone unturned as you assess the quality of your final product.

• Technology agnostic: Functional testing is a black-box method that doesn’t require knowledge of the underlying code structure. This flexibility enables you to test any software component or system.

Cons

• Can’t catch everything: Although essential, functional testing alone isn’t enough. It doesn’t assess code quality, security vulnerabilities, performance bottlenecks, or other non-functional aspects.

• Potentially costly: Planning, documenting, executing, and maintaining functional test cases can be resource-intensive, especially for larger apps with more complex logic.

• Limited defect prevention: Functional testing only confirms your product’s features after you’ve built them. It doesn’t prevent functional defects from being introduced in the first place.

• Updates require retesting: Any modifications or updates to your software require regression testing to ensure existing functionality isn’t broken, adding an extra maintenance burden.

Your functional tests can take many forms depending on the product and the software you use.

That said, most testing efforts follow a similar high-level process with some key steps:

• Requirements analysis: The first step is to thoroughly analyze and understand the specified requirements—i.e., what the product is supposed to do. This could involve reviewing written requirements, user stories, mock-ups, and more.

• Test planning: Once the requirements are well understood, it’s time to plan the test strategy. This involves mapping test scenarios to requirements, defining test cases, deciding which testing techniques to use, outlining the testing environment needs, and determining other logistics.

• Test case development: With the test plan in place, the next step is developing test cases and scripts. These specify the step-by-step actions, test data, and expected results that will validate each requirement.

• Test environment setup: Next, it’s time to run those tests. The documented test cases are carried out manually and/or using automation tools. Detailed notes are taken on the test results.

• Bug reporting and tracking: When a test fails and you find a defect, it must be documented appropriately and logged into a tracking system for follow-up, root cause analysis, and eventual resolution.

• Re-testing: Once you’ve fixed the bugs, the penultimate step is re-testing to ensure the issues are resolved and no regression defects were introduced. This cycle continues until all your tests pass successfully.

• Test closure: With the test objectives met, you can sign the process off and give the go or no-go decision for any product or feature release.

Functional testing itself covers a variety of specific testing techniques and methods. The tests are chosen based on the system being analyzed and your overall testing objectives.

Let’s look at some of the most common testing types:

• Unit testing: This type of functional testing focuses on testing individual units or small parts of a software system in isolation. It verifies that each part meets its design specifications and behaves as expected.

• Integration testing: After unit testing, integration tests prove that the individually tested components work together and with other parts. This might include testing how they communicate and share data with other elements.

• System testing: System tests examine the entire application and its end-to-end scenarios. They take on a user's role from start to finish and check that everything flows as expected.

• Regression testing: Any time you add or change a functionality, you must perform regression tests. This retests previously working features to ensure existing capabilities didn’t regress or break.

• Usability testing: This subjective testing method looks at the user experience and ease of use of the application from the perspective of your end-users. It helps highlight areas of user confusion or friction.

When it comes to actually carrying out these functional tests, you have two main options: manual or automated testing. Both approaches play an important role in a well-rounded functional testing strategy.

Manual functional testing means using human testers to follow up on your test scripts and play with the software—just as a real user would.

This hands-on approach is helpful for more subjective tests where a human eye is needed for observation and opinion, such as assessing user-friendliness. Manual tests are also a good starting point before automated testing.

However, having people re-run the same tests over and over can be a tedious and time-consuming task. People’s attention may slip, they might make mistakes, and your tests can become inconsistent.

Automated testing can help account for those errors. It enables you to run pre-scripted test cases quickly without human intervention.

Once you create the scripts, you can simultaneously run the entire test suite in different environments. This automated approach is beneficial for efficient regression testing.

Although automation can be more expensive upfront, it usually pays off in the long run. You get faster feedback loops, can increase your test coverage, and can enable helpful practices such as nightly build verification.

Most product and testing teams combine manual and automated functional tests. New features might start with manual exploratory testing before moving to automated tests once stable cases are identified. This gives them the best of both worlds—human insights alongside automation muscle power.

Both functional and non-functional testing are vital for delivering a quality product. Functional tests ensure the features meet your requirements, while non-functional tests ensure those same features are secure, perform well, and are stable enough to satisfy more users.

For example, a functional test wouldn’t focus on how quickly your “Submit Order” button processes—only that it works.

However, load testing, a type of non-functional test, would evaluate how the application handles a spike in order volumes. It looks at how well the app works under various real-world scenarios and quality measures.

Non-functional testing examines the more general characteristics and quality attributes that don’t directly relate to functional behaviors. Tests might analyze the product’s performance, security, reliability, and compatibility across different systems.

Functional tests span every domain and application type. Although the tests themselves are unique, they all have the same goal: to confirm that each product feature works as intended for the user.

Whether it’s an ecommerce website, mobile app, enterprise, or even a game, if you expect users to interact with your product, you’ll need clear, functional tests to authenticate and meet their expectations. This prevents you from shipping features into the unknown.

Here are some typical examples of functional tests in action across different domains.

Web app/website testing

• Testing if user registration and login flows work as expected
• Verifying that your ecommerce checkout properly calculates taxes and shipping costs
• Ensuring all links, menus, and navigation elements direct users to the correct destination
• Validating that form submissions show proper success or error messages

Mobile app testing

• Testing that the app installs and launches properly on different devices
• Verifying that core gestures and transitions between screens work smoothly
• Confirming if APIs integrate properly to serve data to the app
• Testing that push notifications are received and behave correctly

Enterprise software testing

• Proving that data imports and exports work for various file formats
• Testing if approval workflows follow the rules for different roles and permissions
• Ensuring the software integrates seamlessly with existing infrastructure
• Checking that report generation tools produced the expected output

Implementing a comprehensive, effective functional testing process for your product means considering a few best practices.

• Keep tests simple and modular: Functional tests should focus on one requirement or function at a time. Trying to test too many things simultaneously makes tests bloated and harder to maintain. Keep them simple, direct, and modular.

• Prioritize based on risk: It’s impossible to test everything equally. Prioritize your efforts based on which features have the highest risk and impact on your users. For instance, a new payment feature might take priority over a minor UI tweak.

• Implement test-driven development (TDD): Developing functional tests before writing code can be a game-changer. With TDD, you get a clear set of tests to code against from the start—this reduces defects and makes testing smoother.

• Use automated tools: Take advantage of automation frameworks and tools to run tests efficiently, consistently, and in parallel across different environments. You can easily carry out hundreds or even thousands of tests simultaneously.

• Enable self-healing tests: Choose automation tools that can auto-adjust your test scripts when applications change. This “self-healing” ability means fewer broken tests.

• Integrate into CI/CD: Don’t treat testing as an afterthought or silo it from developers. Instead, integrate functional tests into your CI/CD pipeline for faster feedback loops.

• Prioritize traceability: Always ensure you can trace your functional test cases to their respective requirements or user stories. This prevents teams from going outside the authorized scope and provides clear quality signoff criteria.

• Review and refine constantly: Testing isn’t a set-it-and-forget-it activity. Consistently review your functional test cases to remove redundancies, add new tests for changed requirements, and optimize its overall coverage.

A powerful A/B testing platform, Amplitude enables you to test and experiment with your product’s features and analyze their functionality and performance in a real-world setting.

The platform provides an unparalleled view of your product’s actual usage. A robust combination of testing and behavior intelligence enables you to confidently deliver the exceptional digital experiences your customers demand.

Use Amplitude to capture rich user behavior data, identify friction points, optimize flows, and validate your intended user experience. Monitor for abnormal patterns, drill into specific user journeys, tie events back to releases, and ultimately iterate faster based on genuine data.