Functional Testing Complete Guide 2021

Functional Testing is one of the types of testing , which assists the team remarkably in verifying the quality as well as the functionality of the software. The functional testing process enables the testing team to validate whether or not the software is fixed and ready for its release. Hence, to define the importance of functional testing, the following is a detailed discussion on the same.

As you are aware of the term functional testing now. By the end of this article you will learn the following:

  • What is Functional Testing?
  • Functional Testing Example.
  • Features of Functional Testing.
  • Functional Testing Types.
  • Functional Testing Process.
  • Writing Functional Test Cases, With Example.
  • Functional Testing Techniques.
  • Functional Testing Checklist.
  • Functional Testing Tools.
  • Functional Test Automation.
  • Functional Testing vs. System Testing.
  • Functional vs Non Functional Testing.
  • Advantages and Disadvantages of Functional Testing.
  • Functional Testing Checklist.

What is Functional Testing?

Functional Testing
Functional testing, as the name suggests, means to check the functionality of the software based on SRS (Software Requirements Specification).The main objective of functional testing is to validate the functionality of the software and ensure that it is in compliance with the business requirements, stated by the client before the commencement of the project.

After the software development stage of a software product is completed, it requires to be tested on the basis of its chief specifications, such as user commands, search operations, and more. This is achieved with the assistance of functional testing, which subtly defines what a system does and validates its accuracy.

Functional Testing Example:

Now that we understand the concepts of functional testing, let us take a practical example of the functional testing.

For example, when a customer checks out of the cart of an eCommerce application, they should be taken to a secure payment page, where they make their payment. To complete this payment, the next step should be taking the customer to bank security verification.

Once they complete these steps, they should receive a confirmation email with details about the purchase, such as the price, delivery date, and more.

The proper functioning and accuracy of these steps are ensured by functional testing. It makes sure that each step follows the other in the correct order, without any failure or payment errors.

Features of Functional Testing:

From verifying the functionality of the software to ensuring its features and components, functional testing has a major role to play in software testing life cycle (STLC). Therefore, to help you better understand the significance of this testing technique, here are some of its features:

  • Functional testing is a process of quality assurance.
  • It validates the functionality of the web applications and ensures that they conform to their specific functional requirements.
  • It is a type of black box testing.
  • The functional test cases are based on the specifications of the component under test.
  • It tests the functionality and the features of the software.
  • Functional testing is not concerned with how the system processes.
  • This type of software testing does not require internal knowledge of the software structure.
  • It verifies the various aspects described in the requirement specification and function specification document.
  • Functional Testing is a specification based testing.

What are the different types of Functional Testing?

Since, functional testing tests various aspects of a software product, the types of testing that are performed under this methodology of software testing are numerous. Therefore, the different types of functional testing are:

  • Unit Tests: Unit testing tests the individual components of the software and validates their performance as per the specified requirements.
  • Integration Testing: Performed with the assistance of stubs and drivers, integration testing involves testing of individual units by combining and testing them in a group. Integration testing aims at exposing issues and defects in the interaction between various integrated units.
  • Sanity Testing: It tests the logical reasoning pertaining to the working of the program. For example, it can check if the result arising out of a calculation is true or incorrect.
  • Smoke Testing: One of the most preliminary of tests, smoke testing reveals the most elementary of errors. It addresses the most basic of functionalities crucial to the working of the product. It addresses questions like, "Can the program run?" "Is the window opening on pressing the click button?"
  • User Acceptance Testing: As the name suggests, user acceptance testing involves creation of a scenario where the targeted customers or the end users get a chance to review the functioning of a product. This can be something as basic as testing the attachment function in Gmail.
  • Regression Testing: Many a times, a bug is revealed in the functioning of an application, post minor variation in its configuration due to an upgrade. This is called a regression. The aim of regression testing is to eliminate any such eventuality and make the product resistant to glitches in the aftermath of a patch or upgrade.

Functional Testing Infographic

Functional Testing Infographics

How to do Functional Testing?

Contrary to popular belief, functional testing can be and should be performed in the beginning of the software development stage. Pretty much a black box testing technique, it involves initial feeding of input data to the system and a subsequent validation of the response, against the main specifications. In short, the functional testing process can be summarized into few important points, which are:

  • The expected functionality of the software product is identified.
  • Test data is utilized by the team to identify the inputs.
  • Once identified, the team creates input data on the basis of the functional specification.
  • Test cases are executed with proper inputs.
  • Finally, the results derived from the executed tests is compared with the expected output.

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Writing Functional Test Cases, With Example:

To ensure thorough coverage during functional testing, it is important to have a well-written functional test case that covers each new feature and function of the software application. These are written by QA managers to test the application's function and ensure it produces the expected output.

A well-written functional test case usually includes the following:

  1. ID: A unique identifier.
  2. Name: The description and name of the function or feature to be tested.
  3. Preconditions: The prerequisites or conditions that must be met to test the feature/function.
  4. Steps: Steps performed to get the end result.
  5. Expected Results: The anticipated results from the test.

Once these details are included, the team can begin writing the test cases by following these steps:

  1. Identification: Identify the areas that need to be tested.
  2. Outline Features: Create a list of all the functions and features that need to be tested.
  3. Categorize: Once the list is prepared, categorize test cases that have to be combined or separated.
  4. Writing Test Cases: After the categorization phase, write test cases into your test management tool using the template defined above.
  5. Delegating Tasks to Testers: Once the test cases are prepared, they are assigned to each tester based on priority, importance, or any other specific testing strategy.
  6. Designing & Allocating Exploratory Testing: To test the software application as a real user include exploratory tests along with the predefined test cases.

Functional Test Case Example:

If you have to create a functional test case to check if an error message appears when invalid input is provided for payment in mandatory fields, it will be written in the following manner:

  • ID: TCE01
  • Description: Entering invalid payment details to check whether the error message appears in the mandatory fields.
  • Preconditions: A payment method should be selected before making a payment.
  • Steps:
    • Select the card type.
    • Enter invalid card number (CVV, Expiration Date, etc.)
    • Click on Submit.
  • Expected Results: It should show an error message for invalid details.

Functional Testing Techniques:

During the process of functional testing, two major techniques are used by the team of testers. Each of these cater to different aspects of the software and work together to improve the quality as performance of the software. These techniques are:

  1. Requirement Based Testing: During this type of testing the requirements are prioritized by the team on the basis of the risk criteria, after which most critical and important features and functions of the software are evaluated and tested.
  2. Business Process Based Testing: This type of functional testing relies on the knowledge of business processes, based on which the scenarios for testing are described.

Apart from these two techniques, functional testing also uses the white box testing and black box testing techniques to run the tests and to ensure the quality as well as the functionality of the software product.

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Functional Testing Checklist:

The importance of creating a check-list before the beginning of any process is quite well known to us. Likewise, it is crucial for us to prepare a functional testing checklist, which can help us track the progress of functional testing.

Therefore, here is a check-list for functional testing.

  • Identify and define the objective of testing.
  • Understand the business requirements and specifications.
  • Bring together a team of dedicated individuals for the process of testing.
  • Create a plan or test strategy before the commencement of the process.
  • Test cases should be designed to stimulate the flow of activities.
  • Prioritize critical features and aspects of the product and test them first.
  • Find an appropriate tool for the process of testing.

Get a detailed overview of functional testing checklist here.

Functional Testing Tools List:

Apart from manual testinga>, the process of functional testing can also be executed with the assistance of various tools available in the market. These tools simplify the process of testing and help the team get accurate and effective results.

Hence, here is a list of important automation tools used for functional testing:

  • Selenium:One of the most popular and powerful test automation tools, Selenium is an open-source functional testing tool supported by the Apache 2.0 license. It is an easy-to-use tool that accepts many languages to write its test scripts like C#, Java, Perl, PHP, Python, Ruby, and more.
  • TestingWhiz: A codeless automation testing tool, TestingWhiz helps automated testing for software, web, mobile, database, cloud, web services, and API testing. The tool effortlessly and efficiently executes and manages test cases and creates robust modular automation scripts using its readily available commands.
  • Coded UI Test.: Coded UI Test or CUI Test is a free, open-source functional testing tool by Microsoft that helps completely automate tests for validating the functionality and the behavior of the application.
  • HP UFT: One of the primarily used functional, regression, and service testing tools, Micro Focus Unified Functional Testing (UFT), formerly known as HP QuickTest Professional, helps testers execute automated tests to identify any errors and discrepancies. It is a simple to use, understand, and navigate tool that provides extended support for mobile testing.
  • TestComplete: A prominent functional automated testing tool by SmartBear Software, TestComplete enables teams to scale their automated testing efforts and maximize test coverage. It helps create automated tests for desktop, web, and mobile applications and supports various applications and technologies like Visual C++, Java, Windows, WPF,.Net, and more.
  • Sahi: Another open-source automation testing tool, Sahi is easy to set up and provides the facility of recording and play backing of scripts. It is a browser and OS independent tool that supports data-driven testing by connecting to Excel or CSV files and languages like Java and JavaScript.
  • TimeShiftX: A date and time shift simulation software, TimeShiftX expedites temporal testing and validates all date & time sensitive functionality and code such as year-end, daylight savings, leap year, billing, rates, policies, etc.
  • SoapUI A most widely-used automated testing tool, SoapUI is an open-source tool for functional, load, compliance, and security testing. It is also used to test and work with Service Oriented Architectures and REST web services. It is a simple tool that includes advanced functionality like a comprehensive view of the project, easy data-driven tests, a powerful HTTP monitor, etc.
  • Waitr An open-source tool developed using Ruby, Watir, tests web applications developed in any programming language. It offers inbuilt libraries to test page performance, alerts, browser windows, take screenshots, etc. It is an easy-to-use tool that supports all the latest browsers.
  • Rational Functional Tester An automated functional testing and regression testing tool by IBM, Rational Functional Tester is capable of performing automated functional, regression, GUI, and data-driven testing. It supports numerous applications like web-based, .Net, Java, Siebel, SAP, PowerBuilder, and more.
  • SilkTest: One of the most preferred tools for maximizing effectiveness, speed, and cost-efficiency of applications, SilkTest enables functional and cross-browser testing easily, with minimum complexity and cost. It supports a broad range of most common technologies and provides the best solutions for web and mobile technologies.

For a detailed list of functional testing tools, click here.

Functional Test Automation:

To perform end-to-end and comprehensive functional testing, organizations worldwide are rapidly switching from manual testing to automation. Automated functional testing, when implemented effectively, turns manual functional testing tasks into hands-off, constantly running processes. It allows teams to run sequential tests and focus on more complex and strategic tasks, which further helps deliver a better application.

Functional test automation uses a computer to run test cases, which saves time, effort and increases overall testing capacity and accuracy.

Today, various functional test automation tools are available in the market that help organizations execute functional tests easily and quickly.

Functional Testing Using Selenium:

Selenium is an open-source test automation tool used for functional testing. It uses test scripts that contain a series of test steps, which are performed on the UI to verify its functionality. Moreover, the test script gives the list of commands to be executed on the UI to interact with different elements.

When the test script passes to the Selenium server, which uses JSON to communicate with the appropriate Web Drive, Selenium Web Driver converts this into interactions with a real browser and returns the result. Finally, the team compares the actual result with the expected result.

Difference Between Functional Testing & System Testing:

Functional Testing System Testing
1. Functional testing is a part of system testing. 1. Tests are executed to verify the compliance of the completed and integrated software with its specifications.
2. Verifies the functionality of the product and ensures it works as per its specifications. 2. Its purpose is to ensure that the completed product fulfills the stated requirements.
3. Tests the functionalities and features of the software, such as load, security, performance and more. 3. It is performed to the test the end product.
4. Manual testing and automation test tools can be used for functional testing. 4. It tests every single module, interface and internal and external aspects of the software.
5.It helps define what the product does. 5.It defines how good a software works.
6. Does not require internal knowledge of the structure. 6. System testing is performed after integration testing and before acceptance testing.

Functional Testing vs Non Functional Testing:

Software Testing LifeCycle (STLC) is an amalgamation of various testing techniques that are divided into two major categories- Functional Testing and Non-Functional Testing. These two testing types are an integral part of any well-designed quality assurance strategy and plan. Hence, let us understand how they are different from one another.

Functional Testing:

Performed before Non-Functional Testing, Functional Testing helps verify each function of the software application to ensure its compliance with key business requirements. It helps validate the application behavior by testing various aspects such as user interface, database, APIs, security, etc. Some examples of Functional testing types are:

  • Unit testing.
  • Integration Testing.
  • Sanity Testing.
  • Smoke Testing.
  • User Acceptance Testing.
  • Regression testing.
  • Localization Testing.
  • Globalization Testing.
  • Interoperability Testing.

Non-Functional Testing:

Another critical testing category, Non-Functional Testing, is performed after functional testing to verify the non-functional parameters of a software application. Designed to test the readiness of the software, non-functional testing is focused on addressing issues that are not covered by functional testing. As non-functional testing validates the application performance, it plays a crucial role in customer satisfaction. Some examples of Non-functional testing types are:

    You can also read about the differences between functional and non-functional testing, here.

    Advantages and Disadvantages of Functional Testing:


    Lets highlight various advantages of Functional Testing.

    • Functional testing is essential for evaluating the performance and the functionality of a software application before it is delivered to the end user for its real use.
    • It is performed from the perspective of the users, which allows the development team to create test scenarios that represent the real world use scenarios.
    • Allows the team to meet the requirements of the user as well as the client.
    • It helps improve actual system usage.
    • Enhances the quality of the software product.


    Listed below are the various disadvantages of Functional Testing:

    • Functional testing can miss critical as well as logical errors in the system.
    • The possibility of conducting redundant testing is high in functional testing.
    • This testing cannot guarantee the readiness of the software to go live.


    From the above discussion, we can easily conclude that to build a strong foundation of a top class software product, functional testing is essential. It acts as a bedrock of the structure and is a crucial part of every test routine.

    Recommended Articles:

    Here I have hand-picked a few articles for you that will help in understanding the broader aspect of software testing:

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