What is Functional Testing? Definition, Types & Examples

When people refer to "testing" in a general context, they often have functional testing in mind. It's about making sure that the core functions are working as they should. The scope of functional testing is so broad that it encompasses so many other types of testing.

In this article, we'll explore the concept of functional testing in-depth, its challenges, best practices, and tools.

What is Functional Testing?

Functional testing is a type of software testing where testers check if features of the application are working as expected according to its specified requirements. These requirements are either collected from the users or provided by the stakeholders (development team or product owner).
 

The primary goal of functional testing is to ensure that the software performs the functions it was assigned to do, and typically does not concern itself with the internal code structure or implementation details. It is one of the most common and foundational types of testing.

Examples of Functional Testing

When testing a web application's Login page, functional testing ensures it works as expected. Key features to test include:

• User Authentication: Validate that users can log in with valid credentials.
• Account Lockout: Check if accounts lock after multiple failed attempts.
• Password Reset: Ensure users can reset their passwords via the "Forgot Password" feature.
• Remember Me: Test if users stay logged in across browser sessions when this option is selected.
• Account Recovery: Verify the process for recovering accounts.
• Multi-Factor Authentication (MFA): Test additional security layers like SMS codes or app-based tokens.
• Session Management: Ensure users are logged out after inactivity for security purposes.
• User Monitoring: Confirm tracking of login activities.
  
  

Read More: 100 Test Cases For The Login Page

Functional Testing vs Non-functional Testing: Key Differences

While indeed accounting for a major part of the test plan, functional testing should not be the only testing type your team performs. Non-functional testing is the much needed counterpart.

1. What is Non-functional Testing?

Non-functional testing is a type of software testing that focuses on evaluating the non-functional such as the system's performance, reliability, and stability.  

When doing functional testing, testers try to answer the question Can the system do what it was built to do? 

When doing non-functional testing, testers try to answer the question Can the system do what it was built to do well enough? 

Here are 5 non-functional test cases for you to better understand the concept:

1. Measure the response time of the system under normal load conditions.
2. Simulate concurrent user connections to determine how the system performs under heavy load, checking for response time degradation or failures.
3. Conduct usability testing with actual users to gather feedback on navigation, intuitiveness, and overall user experience.
4. Assess the system's ability to handle an increased workload by gradually increasing the load and observing performance metrics like CPU and memory usage.
5. Test user roles and permissions to ensure that users can only access the features and data they are authorized for.

2. What are the differences between functional testing and non-functional testing?

Functional testing primarily focuses on whether the system delivered the output desired. 

Non-functional testing validates the “hows” of the AUT’s features, performance, security, scalability, etc.

Here's a quick comparison table for you:

Step 1. Decide on test scenario

Functional testing starts with requirements, which are based on user stories. A user story describes what a user wants and why, serving as the foundation for requirements and test cases.

A typical user story follows this format:

• As a [role]: Who benefits from the feature?
• I want [feature]: What functionality is needed?
• So that [benefit]: Why is it important?

For example:
"As a customer, I want to view my order history online so that I can track my purchases."

This story is a starting point, but it’s not detailed enough for development or testing. Testers must collaborate with users to understand their needs and put the story into a real-world context. By doing so, the story becomes a requirement, which guides development and functional testing.

Breaking Down User Stories

User stories can be too broad. To make them actionable:

1. Break the story into smaller, specific tasks.
2. Define the steps required to achieve the goal.
3. Create testable chunks to reduce risks and speed up coding and testing.

For example, the order history story could be broken into smaller tasks like:

• Displaying a list of past orders.
• Allowing users to filter or sort orders.
• Showing order details, such as delivery status.

Step 2. Write the tests

Here comes the tricky part.

For manual testing, you don’t need to write test scripts, but you still need a test management system to track your test results and progress.

For automation testing, you can write scripts to execute tests automatically. Tools like Selenium or Playwright provide built-in commands and features to make this process easier.

A keyword-driven framework simplifies automation testing. Instead of writing code, testers use pre-defined keywords that represent specific actions. These keywords are grouped together to create tests.

For example, in Katalon Studio’s keyword library:

• Use "Navigate To Url" to open a specific URL.
• Use "Click" to interact with a button or link on the page.

This approach makes writing automated tests faster and more accessible.

One keyword at a time. In no time, you should find yourself with a full test script ready to be executed. Learn more about Katalon Studio here.

Types Of Functional Testing and Examples

Functional testing extends from component-level testing all the way to regression testing of existing features. It finds itself in any type of testing involved with functionality. If you are doing regression testing for a certain feature, that is still functional testing.

Let’s look at some popular testing types:

• Unit Testing – Tests individual pieces of code (like functions or methods) in isolation.
• Integration Testing – Ensures different modules or components work together correctly.
• Smoke Testing – A quick, basic test to check if the main functions of the software work properly after a build.
• Regression Testing – Verifies that recent code changes haven’t broken any existing functionality.
• Exploratory Testing – Testers explore the software freely to discover issues.

Why Automate Functional Testing?

Softwares are powerful. AIs can even paint and write poetry now. If you are not leveraging softwares to test softwares, you are definitely missing out. 
 

Investment into automation testing is the most valuable thing you can do on your testing journey. Functional testing benefits so much from automation. If you embrace TDD, chances are you are writing automated tests so that the dev team can repeatedly re-execute the tests until the feature passes. 
 

With repetitive and time-consuming test cases automated, quality engineers have more time to develop more insightful test scenarios, thoroughly test the product inside-out, and examine the product under edge cases and exploratory testing.

Learn more: What is TDD and how to apply it to your daily testing activities?

How to choose your automated functional testing tool?

Functional testing plays a crucial role and is tied to many other activities in the software development life cycle. However, teams usually use a number of fragmented tools that solve separate testing needs, which creates a collection of complex, brittle, and hard-to-scale tool-stacks for quality management.

This means you have 3 options to do functional testing: 

Option 1: Build Your Own Testing Framework with Open-Source Libraries

• Choose an open-source testing library as the foundation.
• Use libraries, drivers, design patterns, and coding standards to build.
• Requires coding and testing expertise but offers high customization.
• Setup time is significant, but it's budget-friendly.
• Maintenance and issue resolution may extend testing cycles.

Option 2: Single-Point Commercial Automation Testing Tools

• Commercial tools for specific testing purposes.
• Great for focused testing but may lack flexibility as needs evolve.

Option 3: All-in-one software testing solution

• Integrates all testing functionalities.
• Streamlines workflows from planning to reporting.
• Eliminates fragmentation and offers scalability.
• Initially underutilized but adapts to organizational needs easily.

Here's a list of good functional testing tools for your team

Functional Testing in Action With Katalon

Now that you have broken down the user stories into small slices, let's see how you can automate them.

To start, you can download Katalon. In Katalon alone, you can do test planning, write tests, manage them in suites, schedule for execution across environments, and generate test summary reports. This comprehensiveness allows for a lot of customization and flexibility, no matter how complex the application under test is.

Download Katalon and Give It A Try

Once you have downloaded and installed Katalon, navigate to File > New > Project. You can choose the type of testing for this project, either web, API, mobile, or desktop app. 

You have up to 3 modes of test creation:

1. No-code: turn on the Record-and-Playback mode, and record your screen, just like how an end-user would. Katalon automatically turns that sequence of actions into an executable test script.
2. Low-code: leverage the rich library of keywords to craft your test scripts. All you have to do is choose the keyword for the action you want to automate and set the parameters. Switch to Full script mode whenever you want.
3. Full code: write your test scripts in Groovy. Enjoy the customizability along with the simplicity of No-code and Low-code within your hands.

Interested? Have a look at the demo here:

Moreover, Katalon sets itself apart by incorporating cutting-edge, native AI features to enhance functional testing. Users can autonomously generate test scripts from plain language input or use the "Explain Code" feature to add comments to code snippets for better understanding among stakeholders and team members. Check out our pioneering AI features here.

Do your team need a better solution for functional testing? Start now with Katalon Studio.

Download Katalon and start functional testing for free

FAQs on Functional Testing

1. How does functional testing differ from non-functional testing?

Functional testing checks whether an application performs as expected based on defined requirements (e.g., verifying a login process). Non-functional testing, on the other hand, evaluates aspects like performance, scalability, usability, and security that are not directly related to functionality.

2. What is the role of a requirements document in functional testing?

The requirements document serves as the foundation for functional testing. It defines what the application is supposed to do, helping testers create relevant test cases and ensuring that the application meets business needs.

3. How do you decide which features to prioritize in functional testing?

Features are prioritized based on business impact, user frequency, and risk. Critical features like login, payment processing, or data submission typically take precedence over less essential functionalities.

4. Can functional testing include API testing?

Yes, functional testing often includes API testing to validate that APIs perform expected actions, return correct responses, and handle errors gracefully. Tools like Postman or REST-assured are commonly used for this purpose.

5. How does functional testing handle edge cases?

Functional testing includes edge cases by designing test scenarios that push the application to its limits (e.g., entering the maximum number of characters in a field). These tests ensure that the application handles unexpected inputs or conditions correctly.

6. What is the difference between functional testing and regression testing?

Functional testing verifies whether specific features work as intended, often for new or updated functionality. Regression testing checks that existing features still work after changes, ensuring no new bugs are introduced.

7. Is functional testing automated or manual?

Functional testing can be both manual and automated. Manual testing is used for exploratory or ad-hoc testing, while automation is preferred for repetitive test cases to improve efficiency and consistency.

8. What is the role of data in functional testing?

Test data plays a crucial role in functional testing. It’s used to simulate real-world scenarios, validate inputs and outputs, and ensure the application behaves correctly under various conditions, including valid, invalid, and boundary inputs.