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.

What is Functional Testing?

Functional testing is a type of testing to check if features are working as expected according to its 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. Functional testing is one of the most common and foundational types of testing.

Examples of Functional Testing

Here are some of examples of functional test cases on a Login page:

• 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

Non-functional testing is a type of software testing that focuses on evaluating the non-functional aspects of the system, such as:

• Performance
• Reliability
• Stability
• Security

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 4 examples of non-functional test cases:

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.
3. Conduct usability testing with actual users to gather feedback on the UX.
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.

Here is a simple comparison table for the differences between functional testing and non-functional testing:

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. It usually 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.

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.

Step 2. Write Test Cases

Once you have a clear test scenario, the next step is to write test cases. A test case is a set of conditions that testers use to verify whether a feature works as expected.

Each test case should include:

• Test Case ID: A unique identifier.
• Test Scenario: A brief description of what is being tested.
• Preconditions: Any setup required before running the test.
• Test Steps: A step-by-step guide on how to perform the test.
• Expected Result: The outcome that should happen if the feature works correctly.
• Actual Result: The real outcome after execution.
• Status: Whether the test passed or failed.

Read More: How To Write Test Cases? A Detailed Actionable Guide

Step 3. Execute the Test Cases

After writing test cases, testers run them to verify functionality. Execution can be:

• Manual: A tester follows the steps and checks the results.
• Automated: A testing tool executes the steps and compares results.

When running tests:

• Record any unexpected behavior (bugs).
• Take screenshots or logs for failed tests.
• Ensure consistent testing conditions (e.g., same browser, device).

Step 4. Report and Fix Bugs

If a test fails, report it to developers with:

• Bug ID: A unique identifier.
• Summary: A short description of the issue.
• Steps to Reproduce: Clear steps to recreate the bug.
• Expected vs. Actual Result: What should happen vs. what actually happens.
• Severity: How critical the bug is.

Read More: How To Create a Test Report?

Functional Testing Best Practices

1. Write Clear and Simple Test Cases

• Use short, easy-to-understand steps.
• Keep each test case focused on one function.

2. Cover Edge Cases and Negative Scenarios

• Test not only the expected inputs but also unusual and invalid data.
• Check how the system handles empty fields, wrong passwords, or large inputs.

3. Use Real-World Test Data

• Test with realistic usernames, emails, and transactions.
• If testing an e-commerce site, use actual product names and prices.

4. Automate Repetitive Test Cases

• Automate tests that need to run frequently (e.g., login, checkout, form validation).
• Use tools like Selenium, Katalon, or Cypress for UI testing.

Why Automate Functional Testing?

1. Automated tests run much faster than manual testing. Not just that, they can run 24/7 without intervention.
2. Manual testing can lead to mistakes due to fatigue or oversight. Automation testing ensures more consistent test execution.
3. Automated functional testing allows you to cover multiple browsers, devices, and operating systems.
4. Automation testing is particularly helpful for regression testing, which is a highly repetitive testing activity.

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.