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

Uncover the methodologies, best practices, and tools that empower your team to validate software functionality with our in-depth guide to Functional Testing.

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

Another method is to automate the entire functional testing process using test automation tools. You can create automated test cases and execute them using the automated testing tool. It ultimately saves time, cost, resources, and manual effort.

For example, let’s say you have 100 test cases to execute manually. It might take up to 3 days or more based on the resource allotment, tasks, and time. The same testing process with automated testing tools can take up to 1 day or less with minimal resources, effort, and time.

Testsigma, a robust low-code cloud-based AI-driven test automation tool, is an ideal tool for automating functional tests of web, mobile, API, and desktop apps in one place. You can quickly automate every functional test in plain English using NLPs. Try it now for free.

Automated Functional Testing

Functional Testing Types

In this section, we will explore 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

Unit testing is a vital type of functional testing that involves testing the smallest functional and testable unit of code. To ensure the highest quality of software, unit testing is an essential part of the software development process. Below are some key points to keep in mind about unit testing:

  • Unit testing is mostly performed by developers, as it is a white-box testing technique.
  • It is performed during the earliest stages of development, which helps in uncovering defects during the initial development phases.
  • Various techniques are used in unit testing, including branch coverage, statement coverage, boundary value analysis, and decision coverage.
  • Branch coverage ensures that all the logical paths and conditions are covered during testing.
  • Statement coverage ensures that all the statements present in the function or module are traversed at least once during testing.
  • Boundary value analysis creates test data for the boundary values and also for the values that lie just before and after the boundary value and then runs the test case using all the created datasets.
  • Decision coverage ensures that during the execution of control structures like “Do-While” or “Case statement,” all decision paths are tested.
  • There are various tools used for unit testing, such as Junit, Jtest, JMockit, NUnit, and more.

By implementing unit testing, developers can identify and fix defects early on in the development process, which can ultimately help save time and money while ensuring the software is of the highest quality.

2) Integration Testing

During integration testing, the aim is to validate the interaction between two or more unit-tested components of a software system. To achieve this, the following are tested:

  • Communication of commands, data, database calls, API calls, and micro-services processing between the units
  • No unexpected behavior is observed during this integration

There are two types of integration testing: Incremental and Big-Bang. Incremental integration testing involves combining one or more components in stages and testing them until the entire system is successfully tested. There are three approaches to incremental integration testing: Top-Down, Bottom-Up, and Hybrid. The Big-Bang approach, on the other hand, involves integrating and testing all of the components as a whole system.

3) Interface Testing

Interface testing and integration testing are two distinct types of software testing that are performed to ensure the seamless performance of software applications. Interface testing is primarily focused on testing the communication between different interfaces, while integration testing is focused on testing the integrated group of modules as a single unit. During interface testing, the correctness of data exchange, data transfer, messages, calls, and commands between two integrated components are tested. Communication between databases, web-services, APIs, or any external component and the application is also tested during interface testing. There should not be any error or format mismatch during this data or command communication. If any such problem is encountered, it needs to be corrected. In summary, interface testing and integration testing are both essential to ensure that software applications work seamlessly and without any issues.

  •  Interface testing focuses on testing the communication between different interfaces.
  • Integration testing focuses on testing the integrated group of modules as a single unit.
  • Interface testing tests the correctness of data exchange, data transfer, messages, calls, and commands between two integrated components.
  • Communication between databases, web-services, APIs, or any external component and the application is also tested during interface testing.
  • There should not be any error or format mismatch during this data or command communication.

4) System Testing

System Testing is a crucial phase in the Software Testing Life Cycle (STLC) that ensures that all components of the system are seamlessly integrated and working together as per the requirement specifications. This testing technique is a Black-Box testing method that validates the integrated system against the predefined requirements. System Testing is performed in an almost real-life environment and according to real-life usage. It is essential to perform System Testing before the User Acceptance Testing (UAT) to ensure that the system is fully functional and meets the business requirements. The following bullet points summarize the key aspects of System Testing:

  • All components of the system are combined and tested against the requirement specifications (Functional or System).
  • It is a Black-Box testing technique that validates the integrated system.
  • System Testing is performed in an almost real-life environment and according to real-life usage.
  • It is performed before the User Acceptance Testing (UAT) in STLC.

5) Regression Testing

After developers make enhancements or fix code, it’s important to run a regression test suite to ensure that the changes haven’t impacted existing functionalities and haven’t introduced new defects. Here are some key points to keep in mind when it comes to regression testing:

  • Regression test cases are a subset of functional tests that cover major system functionalities.
  • These cases must be updated, added, and deleted according to application changes.
  • Regression test cases are best candidates for automation testing, as they’re run often and require time for execution.
  • Regression test cases to be run can be selected in three ways: run the whole regression test suite, select high-priority test cases from the regression suite, or select cases from the regression suite testing functionalities related to the code changes.

If you’re spending too much time executing the same regression test cases multiple times in a short duration, it’s time to think about automation. Testsigma is an automation testing tool that can help you automate your regression test cases and improve the efficiency of your testing process.

6) 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. Smoke testing is usually done for the builds created during the initial phase of development, which are not yet stable. The goal of Smoke Testing is to verify that the application’s critical functionalities are working correctly, and the build is stable enough to move to 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. Once the Smoke Testing is successful, the application is ready for the next level of testing.

In summary, Smoke Testing is an essential testing technique that helps ensure that the newly released build meets the required quality standards. Here are the key points to remember:

  • Smoke testing is done to verify that the application’s critical functionalities are working correctly.
  • Smoke testing is usually performed on the builds created during the initial phase of development, which are not yet stable.
  • 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.

7) Sanity Testing

Sanity testing is an essential type of testing that covers the major functionalities of an application. It is normally performed on a new build created by developers for a relatively stable application. The main aim of this testing 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. Here are some key points to remember about Sanity Testing:

  • Sanity Testing is mainly focused on the major functionalities of an application.
  •  It is performed on a new build that has been created by developers.
  • The aim of this testing is to ensure that the application is working as expected and meets the basic requirements.
  • It is essential to note that Sanity Testing is not a replacement for other types of testing, such as Smoke Testing or Regression Testing.

8) Acceptance Testing

Acceptance testing is a crucial step in the software development life cycle, which aims to ensure that the developed system meets all the requirements agreed upon during the business requirement creation. This type of testing is performed just after the System Testing and before the final release of the application in the real world. Acceptance testing becomes a criterion for the user to either accept or reject the system, which makes it a crucial step in the software development process. Here are the different types of Acceptance Testing:

User Acceptance Testing: This type of testing is performed by real users to ensure that the application meets their needs and expectations. It is also known as Beta Testing, which is done at the client site.

Business Acceptance Testing: This type of testing is performed to ensure that the application is able to meet business requirements and goals. It is done to ensure that the application is ready for deployment and will help the business achieve its objectives.

Regulation Acceptance Testing: This type of testing is performed to ensure that the developed application does not violate any legal regulations put in place by the governing bodies. It is done to ensure that the application is compliant with legal requirements and can be deployed without any legal issues.

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, 

Testing Techniques

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.

Equivalence class partitioning

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.

Boundary value analysis

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 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.

Functional Test Process

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.


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.

Frequently Asked Questions

What are the types of functional testing?

Why Automate Functional Tests?