Functional Testing : What It is, How to Do & Examples

In the realm of software development, ensuring that an application performs as expected is paramount. That is where functional testing steps in. Functional testing stands as a cornerstone in this pursuit, serving as a critical step in the quality assurance process. It empowers software teams to build robust, reliable software that stands the test of time. 

In this guide, we will discuss everything about functional testing. But, before we dive into the ‘how-to’ of functional testing, let’s talk about the ‘what’ and ‘why.’ 

What is Functional Testing?

Functional testing is a type of software testing that evaluates the functionality of a software application by testing it against the specified requirements. The goal of functional testing is to ensure that the software works as per the desired specifications and performs its intended functions correctly.

In simple terms, it answers the question: “Does the software do what it’s supposed to do?”

Functional Testing Example

Let’s understand how functional testing helps identify bugs with an example. Here, we will use Uber as an example to state functional testing examples.

Now, what will developers and testers test in the Uber app? Consider the tester has to check the user flow when a user tries to book a ride from point A to point B. To do that, the QA team will start creating test cases. Here are the sample test cases.

1. Log in to the application

2. Select the drop location

3. Then, select the pickup location or move the map pointer to point to the correct pickup location.

4. Select the preferred ride.

5. Now, Uber will start looking for nearby rides. Once an Uber driver accepts your request, the app will display details like driver details, bill, pickup time, driver location, vehicle details, driver rating, etc

6. Once Uber confirms the ride details, the booking is successful. 

In the below sections, we will discuss how this can be automated with the help of a test automation tool.

Why is Functional Testing Important?

Functional testing in software testing is important because it helps verify whether your application is working as intended or not. Even if an application passes non-functional tests and performs well, it has to deliver the expected results to be considered functional for end users.

How To Do Functional Testing – Manual and Automated

You can perform functional testing using two approaches: Manual and Automated. Let’s take a look at both these approaches and which is the ideal way to do functional testing,

Manual Functional Testing

In the manual approach, QA testers will manually create and execute functional test cases. They interact with the software application manually to identify and evaluate its functionality. It is expensive, time-consuming, and nearly impossible to identify every bug.

Automated Functional Testing Using Testsigma

Testsigma is a robust low-code cloud-based Gen-AI powered test automation platform that you can use to automate functional testing of web, mobile, API, desktop, and Salesforce apps in one place. You can quickly automate every functional test in plain English using NLPs without writing a single line of code.

Now, let’s discuss the benefits of automating functional testing using Testsigma,

10X Faster Testing: Create, run, and maintain tests on the cloud using low-code techniques without using code.

70% Less Test Maintenance: Auto-healing helps prevent test failures by detecting and remapping elements whenever the UI changes.

Gen-AI Powered Test Authoring: Testsigma Copilot is a Gen-AI assistant for QA teams that provides automated test case and test scenario suggestions within seconds.

Unified Test Automation: Automate your web, mobile, desktop, API, and Salesforce testing in the same platform without switching between different tools for different testing needs.

Zero Setup Time: A simple one-click free sign in to access the cloud platform. There is no hassle of complex setup or configuration, like the case with traditional testing frameworks.

Minimal Learning Curve: Zero setup, easy onboarding, user-friendly interface, AI features, and low-code approach make the platform accessible to both technical and non-technical users.

CI/CD Integration: Test continuously by integrating your automated tests with existing CI/CD and DevOps pipelines. This speeds up your feedback loops and release cycles.

Types of Functional Testing

Now, let’s discuss the different functional testing types that are used to ensure the quality of software and deliver a flawless product to the end-users.

1. Unit Testing
2. Integration Testing
3. Interface Testing
4. System Testing
5. Regression Testing
6. Smoke Testing
7. Sanity Testing
8. Acceptance Testing

Unit Testing

Unit testing is a vital type of functional testing that involves testing the smallest functional and testable unit of code. It is an essential part of the software development process to ensure the highest quality of code. It is performed by developers and is a white-box testing technique.

Integration Testing

During integration testing, the aim is to validate the interaction between two or more unit-tested software components. It focuses on testing the integrated group of modules as a single unit.

Interface Testing

Interface testing checks the correctness of data exchange, data transfer, messages, calls, and commands between two integrated components.

Do not confuse interface testing with integration testing. Interface testing focuses on testing the communication between different interfaces, while integration testing focuses on testing the integrated group of modules as a single unit.

System Testing

System testing is a crucial phase in the Software Testing Life Cycle (STLC) that ensures that all system components are seamlessly integrated and working together as per the requirement specifications.

It is a black-box testing technique that validates the integrated system against the predefined requirements. It is performed in an almost real-life environment and according to real-life usage.

Regression Testing

After developers make enhancements or fix code, running a regression test suite is important to ensure that the changes haven’t impacted existing functionalities or introduced new defects.

Instead of spending too much time executing the same regression test cases multiple times in a short duration, automate regression tests using a test automation platform like Testsigma and improve the efficiency of your testing process.

Smoke Testing

After the development of an application, it is essential to ensure that all major functionalities work seamlessly. Smoke testing is performed for the newly released build to ensure that the application is ready for the next level of testing.

If any major functionality is not working, as expected, during testing – that particular build is rejected, and developers need to fix the bugs and create a new build for further testing. After successful smoke testing, the application is ready for the next level of testing.

Sanity Testing

Sanity testing is performed on a new build created by developers for a relatively stable application. The aim is to verify whether the application is working as expected or not. Once the application passes the sanity testing, it is considered ready for the next level of testing.

Acceptance Testing

Acceptance testing is performed by real users to ensure that the application meets their needs and expectations. It is also called beta testing and is performed by real users in a real-world environment.

Functional Testing Techniques

Testing techniques are methods that help validate that a software application behaves as expected. The following are some functional testing techniques you can use to test your application, 

These techniques vary slightly in the way they divide test data/inputs. Let’s see how they help create test cases.

Equivalence Class Partitioning

In equivalence partitioning, the testers will divide the inputs into classes or groups of data that are expected to produce similar results. It helps reduce the number of test cases and provides a high test coverage.

For example, if an application accepts numerical inputs from 1 to 10, you might choose test cases from three classes, that is, less than 1, between 1 and 10, and greater than 10.

Boundary Value Analysis

Boundary value analysis focuses on testing the boundary values between equivalence classes. It includes testing both the minimum and maximum values along with values just inside those boundaries.

For example, if the application accepts passwords of lengths 8 to 14, then you would test with values like 7,8,14, or 15.

Decision-Based Testing

The decision-based testing technique involves creating test cases based on the decision points or conditions in the code.

That is, you would create test cases to cover every user condition. For example, consider the below scenario,

1. If the user enters the wrong credentials to log in to the application, then the system should throw an error.
2. If the user enters the correct credentials, then the application should redirect the user to the home page.

State Transition Testing

The state transition testing technique helps test systems that can be in different states and can transition from one state to another based on certain conditions. Let’s take the simplest example to understand this: an ATM. It can be in states like “idle,” “card inserted,” “PIN entered,” and so on. And the test cases would cover the transitions between these states.

End-user Tests/System Tests

System testing or end-user testing tests the entire application to check if the application behaves as expected from the end-user’s perspective.

For example, the tester will consider him an end-user and test any application. Let’s take an e-commerce application as an example. 

Now, the tester will use the e-commerce app to browse, add products to the cart, check out, check the order list, and so on. It helps them understand if the application is easy to use or does its job.

Alternate Path Tests

In the alternate path testing technique, the testers will test all the possible scenarios or ways to use the application. They help cover the not-so-used flows or edge cases.

Ad hoc Tests

Ad hoc tests are unplanned tests that are performed without using a specific test case or script. Testers use domain knowledge, intuition, and experience to explore the application to find hidden bugs.

You can use these testing techniques in various combinations, depending on the nature of the application and its requirements. They help ensure that software is thoroughly tested and reliable before its release.

Functional Testing Vs Non-Functional Testing

Functional testing verifies that the application works as expected and aligns with the business requirements. It checks the app’s features and functionality, such as business logic, user interactions, APIs, and databases, to ensure everything works correctly. 

Non-functional testing evaluates how well an application performs in terms of performance, security, reliability, and other non-functional aspects. It ensures the application works under different conditions. 

To keep it simple, functional testing checks “Does the app work?” while non-functional testing checks “How well does the app work?”

Functional Testing Process: Typical Steps

Functional testing involves testing the application’s UI, APIs, databases, and functionality. The below steps depict how testers usually perform functional testing manually or using automated testing tools. Though, these steps may vary from project to project. Let’s dive in.

Step 1 – Requirements Analysis

Understand and analyze the functional requirements of the software.

Step 2 – Test Planning

Create a detailed test plan based on these requirements. Identify the functionalities that need to be tested. Define the testing environments and tools required. Select a perfect test automation platform that fits your development pipeline.

Step 3 – Test Case Design

Write detailed test cases that cover all the functional aspects of the software.

Step 4 – Test Data Preparation

Create test data that will be used for testing. It may include valid and invalid input data for negative and positive testing.

Step 5 – Execute Tests

Run the test cases according to the test plan. Log the actual results, including any deviations from the expected results.

Step 6 – Compare Results

Now, compare the actual test results with the expected test results.

Step 7 – Test Reports

Once you have analyzed the test results, create a detailed test report outlining the test cases’ status.

Once the developers fix the reported defects, retest the application to ensure it is free of bugs. This repeated testing is called regression testing. 

Testsigma supports automated regression testing as well, along with other types of functional testing. So, you can quickly reuse or update the test cases to ensure that new changes or fixes do not introduce new bugs or break existing functionalities.

Benefits of Functional Testing

Some of the advantages of functional testing include,

• It will help identify bugs or inconsistencies in the application. 
• You can provide users with a pleasant and positive user experience with thorough functional testing. 
• Functional testing and regression testing go hand in hand. It is crucial for maintaining the application’s stability as it ensures that new code changes or bug fixes do not break existing functionalities. 
• With functional testing, you check the entire application’s features and functionality, like UI, API, database, integrations, etc. API functional testing is crucial to ensure the client/server communications work properly.
• While functional testing mainly focuses on testing the features and functionalities, it can also help identify certain security issues, such as authorization issues, input validation problems, and so on.
• It improves the overall quality and stability of the application. 
• When you make sure that the software works correctly and meets user expectations, it leads to high customer satisfaction. It helps build trust and maintain a positive reputation in the market.

Read more: Functional and integration testing are vital to validate the software works as expected. Learn the difference between functional and integration testing here.

Limitations of Functional Testing

Though it offers multiple advantages, it has its limitations. Here are some limitations of functional testing,

• There is a high chance that testers may miss critical and logical bugs during the testing process.
• It has only limited scope. That is, it does not handle non-functional aspects such as performance, scalability, usability, and security.
• Testers may not always think of every edge case or unusual scenario. It could lead to missing critical defects that may slip into production.
• Creating and maintaining functional test cases for complex applications can be challenging and time-consuming. In such cases, automated testing may be more efficient and fast.

While functional testing is crucial, it also has its limitations. Combining it with other testing approaches, such as non-functional testing, can help ensure more comprehensive software testing.

You can learn more about the difference between functional and non-functional testing here.

Best Practices for Functional Testing

Some of the best practices for functional testing that help maintain software quality, identify defects early, and deliver a reliable product are as follows:

1. Embrace Test Automation

Use test automation tools like Testsigma to automate your end-to-end functional testing for your web, mobile, API, and desktop apps. These allow you to easily create and manage more test cases on the cloud by saving time, cost, effort, and resources.

2. Choose Test Cases To Automate Wisely

Do not automate every test case. So, what to automate? Take a look,

• Frequently run test cases
• High-priority test cases (P1, P2) that are time-consuming.
• Tests with varying data sets or inputs.
• Cross-browser, cross-platform tests, and such
• Tests that are prone to human error.

3. Have a Dedicated Team of Automation Testers

Automating testing tasks require specific skills and expertise. Evaluate your QA team’s skill set and assign automation tasks to those who excel in test script creation and tool usage, as not everyone may possess these skills. 

However, using scriptless test automation platforms solves this problem and makes testing accessible to everyone involved in the team (both technical and non-technical). This, thereby, improves the feedback cycles and makes testing an inclusive task.

4. Perform Data-Driven Testing

Create automated test cases that can be used with different sets of data. Testsigma supports data-driven testing, so leverage low-code testing for faster yet efficient testing.

5. Test on Real Devices and Browsers

Test on real devices and browsers to get accurate results. However, testing manually on thousands of devices is impractical. Use a real device cloud to test various conditions that mimic the real-world environment. Testsigma’s real device cloud allows you to test your mobile, web, and desktop apps on 3000+ real devices/tablets and 1000+ browser/OS combinations.

6. Test Frequently

Create reusable test cases and run them every time there is a change in the code. This helps identify regression bugs easily and fix them in no time. Also, integrate your automated tests into the DevOps and CI/CD pipeline for continuous testing and rapid feedback cycles.

7. Shift Left Testing

Implement a shift left approach for testing. It helps test early and fix bugs at the early stages of SDLC, which helps save time and cost involved in bug fixing.

Conclusion

Functional testing is the backbone of software testing that ensures that software applications not only meet requirements but also deliver an excellent user experience. It validates that every component of the software works as expected.

To perform functional testing effectively, you have to follow a structured approach. This includes thorough planning, test case design, execution, and reporting. 

Use automated testing to improve the quality of testing. Choosing a perfect test automation platform plays a vital role in automating tests quickly and efficiently.