When people refer to "testing" in a general context, they often mean functional testing. It's about making sure the core functions work as expected.
In software development, functional testing verifies whether a system meets its functional requirements. These requirements come from users or stakeholders such as the development team or product owner.
The primary goal is to ensure the software performs the functions it was designed to do. It is one of the most common and foundational types of testing.
Functional testing starts from features. For example, when testing a Login page, ask: “What features does a Login page have?” Each answer becomes a test case.
Here are examples of functional tests:
📚 Read More: 100 Test Cases For The Login Page
Non-functional testing evaluates the non-functional aspects of a system, such as:
Functional testing asks: “Can the system do what it was built to do?”
Non-functional testing asks: “Can the system do what it was built to do well enough?”
Examples of non-functional test cases:
| Aspect | Functional Testing | Non-Functional Testing |
|---|---|---|
| Purpose | Verify the software functions as intended and meets requirements. | Evaluate performance, security, usability, and other quality attributes. |
| Focus | What the software should do. | How well the software performs its tasks. |
| Behavior | Tests if the features of the software perform as expected | Tests how well the software performs certain functions or behaves under specific conditions. |
| Scope | Typically focuses on specific features or functionalities. | Covers a broader range of attributes beyond functionality. |
| Examples of Testing Types | Unit Testing, Integration Testing, System Testing, User Acceptance Testing. | Performance Testing, Security Testing, Usability Testing, Compatibility Testing. |
| User Focus | Ensures the software meets user needs and expectations in terms of features. | Ensures the software meets user expectations related to performance, security, usability, etc. |
| Objective Measurement | Often involves binary outcomes (pass/fail) based on expected behavior. | Often involves quantitative measurements and benchmarks for performance or other attributes. |
| Tools and Technologies | Functional testing tools include Selenium, JUnit, TestNG, etc. → Check out the top functional testing tools |
Non-functional testing tools include JMeter, OWASP ZAP, LoadRunner, etc. |
Let’s look at some popular functional testing types:
Functional testing begins with functional requirements, based on user stories.
User stories follow this format:
Example: “As a customer, I want to view my order history so I can track my purchases.”
Testers refine broad user stories into specific, testable requirements by breaking them into smaller tasks, defining steps, and creating testable units.
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:
📚 Read More: How To Write Test Cases?
Execution may be:
During execution, testers capture bugs, screenshots, logs, and ensure consistency across environments.
A good bug report includes:
📚 Read More: How To Create a Test Report?
When writing functional test cases, the first best practice is to keep them clear and simple. Each test case should have short, easy-to-understand steps, with the scope limited to one function at a time. This reduces ambiguity and ensures other team members can quickly grasp the purpose of the test.
A second best practice is to make sure you cover edge cases and negative scenarios. It’s not enough to only test expected inputs, you should also verify how the system handles unusual or invalid data.
For example, on a Login page, edge cases could include leaving both the username and password fields empty, entering a password that’s far longer than expected (e.g., 256+ characters), trying unsupported characters like emojis, or attempting to log in with an SQL injection string to test security.
You could also test what happens when the account is locked after too many failed attempts, when the session times out mid-login, or when the network drops right after pressing “Login.” These aren’t everyday scenarios, but they simulate real-world conditions and reveal how resilient the system is.
Third, use real-world test data whenever possible. Functional tests become much more valuable when they mirror realistic user activity.
For example, when testing a login form, you should use usernames and emails that reflect actual usage patterns. If you’re testing an e-commerce system, include real product names, prices, and transaction-like data to better simulate real-world workflows.
Finally, automate repetitive test cases to save time and reduce human error. Tests that need to run frequently, such as login, checkout, or form validation, are strong candidates for automation. Tools like Selenium, Katalon, or Cypress are commonly used for UI-level automation and can be integrated into CI/CD pipelines to ensure fast, reliable feedback.
📚 Read More: A guide to automate functional tests