What is Functional Testing? Definition, Key Concepts, & Types

In this article, we’ll delve into the essence of functional testing — its definition, purpose, and the incredible value it offers.

As software developers, we know the importance of writing code that works correctly. But even the best code can have bugs. That’s where functional testing comes in.

What is Functional Testing?

Functional testing ensures that software meets its requirements. It does this by testing each individual function of the software to make sure it works as intended. It’s like giving the software an extensive check-up. You want to see if it behaves just the way it’s supposed to. With functional testing, you test different software parts to see if they do what they’re meant to do.

Importance of Functional Testing in Software Development

Testing software helps find any mistakes or problems — ideally before you’ve released your app to the public. You can ensure it works great, has no errors, and does what it should.

Testing saves time and money. Fixing software issues after release can be costly and time-consuming. For example, if a software application has a security vulnerability, it could be exploited by hackers to steal data or cause other damage. So, for a good software developer, functional testing is like ensuring your software is safe to use.

Key Concepts of Functional Testing

There are several key concepts involved in functional testing, which we’ll list below.

Understanding the software functionality

The first step in functional testing is understanding how the software should work. This means understanding what the software does, its features, and how users should use it. As a functional tester, you can do this by reading the software’s documentation, talking to the developers, and using it yourself.

Identifying functional requirements

Secondly, you need to understand how the software is supposed to work, you need to identify the functional requirements, which are the specific actions that the software is supposed to do. For example, a functional requirement for a game might be that it has to have ten levels or that it has to allow players to play against each other online.

Test scenarios and test cases

Again, as soon as the functional requirements are identified, you must create test scenarios and cases. Test scenarios are descriptions of how the software is supposed to be used. For example, a test scenario for a game might be “Start a new game, play the first level, and win the game.”

On the other hand, test cases are specific steps that functional testers follow to test the software. For example, a test case for the game might be “Click on the Start Game button, select a level, and click on the Play button.”

The actual functional testing

Once you’ve created test scenarios and cases, you can start functional testing. Functional testing is the process of using test scenarios and cases to test the software. It involves using the software in all the different ways a user might use it to ensure it works correctly each time.

Reporting bugs

Finally, if you find any problem with the software, you need to report them to the developers. The developers will then fix the problems before releasing the software to users.

Types of Functional Testing

There are different types of functional testing, each with its purpose and scope.

Unit testing

Unit testing is the most basic type of functional testing. It’s done by testing individual code units, such as functions or classes. Unit testing is important because it helps to find bugs early in the development process when they are easier to fix.

You can read up on unit testing for JavaScript here and here (using Mocha and Chai), Python, and React on SitePoint.

There are many different unit testing tools and frameworks available. Some popular tools include JUnit, NUnit, and xUnit. When unit testing, you should focus on testing the following:

• Input. Ensure the function or class accepts the correct input data.
• Output. Make sure the function or class produces the correct output data.
• Boundary conditions. Test the function or class at its boundaries, such as with large or small input values.
• Error conditions. Find out what happens when the function or class is given invalid input data.

Integration testing

Integration testing is done by testing how different units of code interact with each other. This type of testing is important because it helps find bugs when different software parts are combined.

You can read more about integration tests with JavaScript on SitePoint.

There are many different integration testing techniques and approaches. Some popular techniques include top-down integration testing, bottom-up integration testing, and sandwich integration testing.

When performing integration testing, it’s important to focus on testing the following:

• Interfaces. Make sure that the interfaces between different code units are compatible.
• Data flow. Ensure data flows correctly between different code units.
• Error handling. Implement robust error handling in the software.

System testing

System testing is done by testing the entire software system as a whole. It’s important because it helps find bugs occurring when different software parts are used together.

There are many different system testing techniques. Some popular techniques include black-box testing, white-box testing, and usability testing.

When system testing, you should focus on testing the following:

• Functional requirements. Ensure the software meets all of its functional requirements.
• Non-functional requirements. Verify that the software meets all non-functional requirements, such as performance, security, and usability.
• Usability. Confirm that the software is easy to use.

Acceptance testing

Users or customers do acceptance testing to verify that the software meets their requirements. Acceptance testing is important because it helps to ensure that the software is ready for use by its intended audience.

You can read more about acceptance testing using Selenium and PHPUnit on SitePoint.

There are two types of acceptance testing you should know: the user acceptance testing (UAT) and alpha and beta testing.

• User acceptance testing (UAT). UAT is done by users or customers to verify that the software meets their requirements. UAT is typically done after system testing.
• Alpha and beta testing. Alpha testing is done by a small group of users or customers to find bugs and usability problems. Beta testing is done by a larger group of users or customers to find bugs and usability problems and to get feedback on the software.

During acceptance testing, you should focus on the following:

• Functional requirements. Ensure that the software meets all of its functional requirements.
• Non-functional requirements. Confirm that the software meets all of its non-functional requirements, such as performance, security, and usability.
• Usability. Make sure that the software is easy to use.

Regression testing

Regression testing is done by re-testing the software after changes have been made to it. It’s vital, because it ensures that software changes do not introduce new bugs.

You can read about regression testing with PhantomCSS on SitePoint.

There are many different regression testing techniques. Some of the popular techniques include manual regression testing, automated regression testing, and continuous integration and continuous delivery (CI/CD).
When carrying out regression testing, you should focus on testing the following:

• Changed code. Be careful so that the changes to the code do not introduce new bugs.
• New features. Confirm that the new features work correctly.
• Bugs that have been fixed. Make sure that the bugs that have been fixed do not reappear.

Functional Testing vs Non-Functional Testing

When software is being developed, it’s important to ensure it works properly. Two main types of testing are used to do this: functional testing and non-functional testing. Functional testing focuses on the software’s features, while non-functional testing places emphasis on how well the software works.

It’s important to address both functional and non-functional testing when developing software to ensure the software is reliable and user-friendly.

The Functional Testing Process

Functional testing ensures the software caters to the needs of users and that it’s free of defects.

You can read more about functional testing with Nightwatch.js and with Symfony on sitePoint.

Test planning and strategy

The first step in functional testing is to plan and develop a strategy, and this involves identifying the features and functionality of the software that needs to be tested and the types of tests that will be performed. The test plan should also include a timeline for testing and needed resources.

Test case design and preparation

Once the test plan is in place, the next step is to design and prepare test cases. Writers document how they’ll test a particular feature or functionality of the software using test cases. Test cases should be written clearly and concisely.

Test execution and reporting

After preparing test cases, the next step is to execute them, and this involves running the software through the test cases and recording the results. The development team should receive a report on the results of the test execution, which should include a summary of the results, as well as any defects that were found.

Defect tracking and management

Upon receiving the reports on the defects, the next move should be assigning the defects to developers and tracking their progress until they are fixed. It’s also important to communicate the status of the defects to the stakeholders.

Challenges of Functional Testing

Functional testing can present challenges such as these:

• Time constraints. Functional testing can be time-consuming, especially for large or complex software applications.
• Resource constraints. It requires a lot of resources, such as testers, test data, and test tools.
• Changing requirements. There can be frequent alterations to requirements during software development, making it difficult to keep functional tests up-to-date.
• Defects. Functional tests can find defects in software, but not all defects can be found.

To overcome these challenges and become a testing pro, it’s important to follow some best practices for software development:

• Thorough planning. Create a master plan. Thorough test planning helps to understand the software better and identify potential challenges upfront.
• Clear test cases. Crafting well-defined and clear test cases is like creating a manual. It helps to ensure that every part of the software is tested properly.
• Automation magic. By automating repetitive tests, focus can be directed to more challenging tasks. Test automation can save time and effort.
• Continuous learning. It’s important to keep learning and growing. In functional testing, continuously learn new techniques, tools, and technologies to stay ahead.
• Test data management. Test data is essential for functional testing. It’s important to manage test data carefully to ensure that it is accurate and up to date.
• Collaboration and communication. Functional testing is an iterative process that involves collaboration between testers, developers, and other stakeholders. Communicating effectively throughout the testing process is vital to ensure everyone is on the same page.

Tools and Frameworks for Functional Testing

There are various tools and frameworks that automate the testing process and enable us to execute tests more efficiently and effectively.

Some of the most popular tools include:

• Selenium. A free and open-source tool for automating web-based functional testing.
• TestComplete. A commercial tool for automating functional testing of desktop, mobile, and web applications.
• Rational Functional Tester. A commercial tool for automating functional testing of desktop and web applications.
• Katalon Studio. A free and open-source tool for automating functional testing of web applications.

Comparative Analysis of Key Tools

When choosing a functional testing tool, it’s good to examine the pros and cons of each tool. Here’s a comparative analysis of the key functional testing tools.

Feature	Selenium	TestComplete	Rational Functional Tester	Katalon Studio
Cost	free	commercial	commercial	free and open-source
Platforms	web	desktop, mobile, web	desktop and web	web
Languages	Java, Python, C#, Ruby	Multiple	Multiple	Multiple
Object repository	Yes	Yes	Yes	Yes
Reporting	Yes	Yes	Yes	Yes
Automation capabilities	Scripting	Record and playback	Scripting	Scripting

Factors to Consider When Choosing a Tool

When choosing a functional testing tool, it’s essential to consider several factors, including:

• Compatibility. The tool should be compatible with the tested application and the platforms it will use.
• Integration. It should combine seamlessly with other tools and frameworks used in the development and testing.
• Ease of use. Should be easy to set up and use, with a user-friendly interface and precise documentation.
• Technical expertise. The tool should match the level of technical expertise of the development and testing teams.
• Cost. It should be cost-effective and provide value for money.

What to Test in Functional Testing

Functional testing is a crucial step in the development process of a bespoke software. But what exactly should be tested in functional testing?

• User interfaces and navigation. This is one of the essential things to test. It involves verifying that the application’s interface is user-friendly and easy to navigate, and this includes ensuring that all buttons and links work as intended and that the interface is responsive.
• Input validation and data integrity. These are essential to functional testing, and they entail testing the application’s ability to validate user input and see to it that it doesn’t contain errors or invalid data. They also test the application’s ability to handle large data sets, while ensuring that the data is always accurate and up to date.
• Business rules and logic. The application’s business rules and logic are critical components that should be tested during functional testing. It involves verifying that the application’s logic is correct and functions as intended. It also tests the application’s ability to handle complex business rules and logic and ensuring that it produces accurate results.
• Error
  handling and exception scenarios. These are crucial components that should be tested during functional testing. They test the application’s ability to handle errors and exceptions, while providing the user with clear and concise error messages. It also ensures that the user is always aware of any issues and can also resolve them.
• Integration points and data exchanges. The application’s integration points and data exchanges are essential components that should be tested during functional testing. It involves verifying that the application can seamlessly integrate with other systems and applications and exchange data accurately and securely.

Conclusion

By testing different app parts, such as its user interface, functionality, and performance, developers can spot and fix issues before making the application available to the public. Using the right tools and following best practices when conducting functional testing is vital to ensure the app is high-quality, easy to use, and fun for users. With functional testing, developers can create apps that meet user expectations and provide a great user experience.

FAQs about Functional Testing