What is Functional Testing?

May 7, 2024

In this guide, we explain functional testing, what it is, the types and how to maximize it using Functionize. Learn more about functional testing here.

In this guide, we explain functional testing, what it is, the types and how to maximize it using Functionize. Learn more about functional testing here.

Functional testing is a form of software testing where you check that your application does what it’s supposed to. In effect, it’s a form of black box testing because you are only concerned with what it does, not how it does it. This is different from unit and integration testing, where you also care about how the software works. 

Functional testing should test your application from a user’s perspective, however, it’s not the same as user acceptance testing. It can happen at any stage in the development cycle once you have working code to test. Without functional testing, you can’t know that your application meets its requirements. It may pass all unit tests and non-functional tests with flying colors. But if any functionality is broken, the whole application is broken. 

This means that you have to plan your testing really carefully. Every user journey should be tested, including ones that might be unusual or non-obvious. Doing this requires cooperation between the product team (who understand what the application should do) and the test team.

What Does Functional Testing Do?

  • is about the functionality of your application, not how it achieves it.
  • is testing against the business/design requirements of your application.
  • is about what the user sees and experiences, but is not the same as user acceptance testing.
  • is not interested in the performance and reliability of your application.
  • s generally black box.
  • can happen at any stage in the development cycle, but generally is done during system and acceptance testing.
  • should test all the moving parts of your code. This requires careful thought and test planning.
  • should use carefully designed test data with known expected outcomes. This should come from the requirements/design.
  • is an essential part of any test plan.
  • can be automated relatively easily.

Functional Testing vs. Non-Functional Testing

Functional testing doesn't check the quality, security, or speed of the code like non-functional testing does. It's more about making sure the application meets what users expect it to do. Functional testing aims to ensure your software operates as intended by checking if the application performs its specified functions correctly. Here, the emphasis is on what the software does, mirroring user interactions. 

On the other hand, non-functional testing looks at things like performance, scalability, and security, which are important for how well the software works overall. Functional testing checks if the software does what users need. Non-functional testing makes sure it does so smoothly and consistently, under various conditions.

Aspect Functional Testing Non-Functional Testing
Focus Checks if the software meets user requirements and performs tasks correctly. Evaluates how well the software performs under various conditions.
Concerns Mainly concerned with what the software does. Concerned with how well the software performs.
Examples of Tests Unit Testing, Integration Testing, User Acceptance Testing. Performance Testing, Security Testing, Usability Testing.
Goals Ensures the application functions according to specifications. Ensures the application performs efficiently and reliably.
Metrics Test cases are based on user requirements and expected behavior. Metrics include speed, scalability, reliability, and security.
Validation Criteria Tests against expected outcomes and user interactions. Tests against performance benchmarks and reliability standards.

Functional Testing Types

Functional testing includes different types, each with specific purposes to ensure the software works as expected. Here's a quick look at some common ones:

  • Unit Testing: Tests individual components or modules to validate they function correctly in isolation.
  • Regression Testing: Verifies that recent changes to the codebase haven't adversely affected existing functionalities.
  • Sanity Testing: Quick checks to ascertain whether a new build is stable enough for further, more comprehensive testing.
  • Smoke Testing: Verifies the basic functionalities of the software to determine if further testing is feasible.
  • Integration Testing: Assesses how well individual components work together to form larger functionalities.
  • Usability Testing: Evaluates how user-friendly the software is by observing user interactions.
  • User Acceptance Testing: Tests conducted by end-users to determine if the software meets their requirements and expectations.
  • Interface Testing: Validates interactions between different software modules or systems.
  • System Testing: Tests the entire system as a whole to ensure all components work together seamlessly.
  • White-box Testing: Examines the internal structure and code of the software to identify defects.
  • Black-box Testing: Tests the functionality of the software without knowledge of its internal workings.
  • Grey-box Testing: Combines elements of white-box and black-box testing, with partial knowledge of the internal workings.
  • Database Testing: Checks the integrity, accuracy, and performance of the database system.
  • Adhoc Testing: Informal testing conducted without predefined test cases or plans to uncover defects.
  • Recovery Testing: Evaluates how well the software recovers from crashes or failures.
  • Static Testing: Analyzes the code or documentation without executing it, often through reviews or inspections.
  • Component Testing: Focuses on testing individual software components to ensure they meet specifications.

Steps to Perform Functional Testing with Functionize

  1. Define testing goals: These goals outline the expected features of the software based on project requirements. They ensure that the application functions as intended and handles errors and unexpected situations smoothly.
  2. Develop test scenarios: Create a comprehensive list of test scenarios for each feature. These scenarios describe how the feature will be used in different situations. 
  3. Prepare test data: Generate test data that mimics real-world usage based on the identified test scenarios. This data can be entered manually or automatically through scripts or test tools. Each set of data should have expected outcomes associated with it.
  4. Design test cases: Develop test cases based on the expected outcomes for the test inputs. For instance, if entering an invalid credit card number, the application should provide a meaningful error message.
  5. Execute the test cases: Run the test cases through the application and compare the actual outcomes with the expected results. Any discrepancies indicate a failed test, and defects should be recorded.
  6. Manage defects: Record identified defects in a formal tracking system accessible to the project team. Make necessary changes to the application and re-run the test cases to confirm resolution before closing the defect.

How do Automated Functional Testing tools work?

When you use automated functional testing tools, they work by interacting with the user interface of the application you're testing. These tools can identify objects on the screen, like buttons and text boxes, and perform actions such as entering data and making selections. 

You might find that many of these tools have a recorder feature, which watches your interactions with the application and records the actions you take. Then, it can replay those actions to replicate your activities. The tool compares the outcomes of these actions with the expected results defined by you or the automation engineer to determine if the test passed or failed. You can either build tests step-by-step using recognized objects or start with a recording, customizing steps and data parameters to suit different environments, including various browsers and mobile devices.

AI in Functional Testing

In functional testing, you'll find that top test automation tools now come packed with artificial intelligence (AI) features. These smart tools use fancy tech like machine learning and computer vision to recognize on-screen elements just like a human does. They can interact with and control objects naturally, making it easier to write tests in plain English.

AI-powered functional test automation has some real benefits. It speeds up test creation, covers more ground, makes testing assets stronger, and reduces the time you spend on maintenance tasks.

Functional Testing Best Practices

When it comes to functional testing best practices, there are some important steps you should take:

  1. Be selective with your test cases: Focus on automating tests that need to be run frequently, involve different data sets, or are prone to human error. Prioritize tests that require a lot of time and effort.
  2. Form a dedicated automation team: Assign automation tasks to team members who have the right skills and knowledge. Take a look at everyone's expertise to make sure tasks are given to the most capable individuals.
  3. Use data-driven testing: Create automated tests that can handle multiple sets of data easily. Store your test data in formats like XML or text files, or retrieve it from databases to make your tests easier to maintain and more efficient.
  4. Be ready for UI changes: Expect that the user interface might change and write your test cases in a way that allows them to adapt easily to these changes. This will help you avoid widespread test failures.
  5. Test often: Make a set of automated tests that you can run regularly. This will help you catch bugs sooner and improve the overall reliability of your testing process.
  6. Test on real devices and browsers: Make sure your testing reflects real-world conditions by using a variety of devices and browsers. This will give you a more accurate picture of how your application performs in different environments.

In conclusion

  • Functional testing ensures your software operates as intended, focusing on what it does rather than how it works.
  • It's crucial for verifying that your application meets user requirements and functions correctly from a user's perspective.
  • Automated functional testing tools use AI capabilities to interact with the application's user interface, making testing more efficient and reliable.

About the author

author photo: Tamas Cser

Tamas Cser


Tamas Cser is the founder, CTO, and Chief Evangelist at Functionize, the leading provider of AI-powered test automation. With over 15 years in the software industry, he launched Functionize after experiencing the painstaking bottlenecks with software testing at his previous consulting company. Tamas is a former child violin prodigy turned AI-powered software testing guru. He grew up under a communist regime in Hungary, and after studying the violin at the University for Music and Performing Arts in Vienna, toured the world playing violin. He was bitten by the tech bug and decided to shift his talents to coding, eventually starting a consulting company before Functionize. Tamas and his family live in the San Francisco Bay Area.

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