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A Complete Guide to Functional Testing

A Complete Guide to Functional Testing

May 23, 2022
Prathitha IyengarPrathitha Iyengar
Prathitha Iyengar

Testing is an essential aspect of application development and helps ensure the app that you are building is stable and works well. It helps you test for usability, accessibility, and performance, so when your users receive the app's final version, they can be sure that it works seamlessly.

Testing also helps you ensure that users get the desired result when they perform a specific task; this is crucial because 70% of online shoppers will abandon their carts because of poor UX. (Kinsta via UXCam).

Functional testing addresses this particular aspect of the user experience. Here's everything you need to know about it.

Measure multi-channel experience monitoring KPIs on real devices and real networks around the world. Learn more!

What is Functional Testing?

Introduction To Functional Testing

The functional or requirement specifications help define what QA engineers consider acceptable while running functional tests. These specifications are a document that tells the QA engineers what actions they must take to determine the conformance of the software system. This document can also ask them to run tests on specific business side scenarios for an overall system picture. 

Hence, we understand that QA engineers can carry out functional testing in two ways:

  • Requirements-based functional testing: This method contains instructions on validating the software system's functional aspects.
  • Business scenarios-based functional testing: This method contains instructions on validating the software system based on business scenarios.
Also read: What Are The Benefits of Using Automated Functional Testing?

Functional testing is software testing that ensures a software system works according to its given specifications. This test's primary goal is to test the functional aspects of the application's software by providing the input and verifying the output based on requirements.

This test does not concern itself with the application's source code and mainly involves black box testing. It checks the APIs, security, client/server communication, database, UI, and other application functionalities. Testers can run functional tests either by using automation or manually.

What do you test in Functional Testing?

Testers primarily run functional testing to check the software system's functionalities. The areas this testing concentrates on are:

  • Accessibility: Runs accessibility checks on the system to see if it meets accessibility requirements.
  • Error Conditions: Whenever there is an error, the system usually provides a valuable error message. This test validates that your system works well and provides the appropriate error messages to debug.
  • Mainline functions: The system has no value if its main functions do not work well. This testing runs to ensure this does not happen.
  • Basic Usability: The test runs a usability test to ensure that users navigating your system can do so seamlessly.
Also check out: Functional Test Automation 101 - How & When to Start

What Are The Different Functional Testing Types?

There are many types of functional testing. Here are a few of them:

Unit Testing

Developers perform unit testing. The developers write test scripts that help testers identify if individual units of a software system match specific requirements. Typically, this involves the developer writing tests that check each unit method and validate these units based on the returned values.

Code coverage is an essential aspect of unit testing. When you're running a unit test, ensure that your test cases cover the following:

  • Line coverage
  • Code path coverage
  • Method coverage

Smoke Tests

Smoke testing, also called build verification testing, ensures the stability of your build, and testers run it after the release of each build. 

Sanity Tests

Testers perform sanity testing to ensure the smooth working of all vital functionalities within your software system. Testers usually run sanity tests after smoke tests.

Regression Tests

Regression tests ensure that the software system remains stable and works according to requirements even when developers add new code, fix bugs, or make enhancements. You don't have to make regression tests as extensive as functional tests. However, you should ensure that your test should help you certify that your system functionality is stable.

Integration Tests

Integration tests help validate the system's functionality when there are multiple modules. These modules may work well individually; however, can they work seamlessly to ensure an end-to-end scenario when clubbed together? Integration tests help answer this question.

Usability Testing

In usability testing, the organization gives real users access to their product and allows them to run tests on it. This test aims to understand how the users interact with the product and if they are comfortable using it. The organization uses the feedback received to make improvements where necessary.

Recommended Post: Unit, Integration, and Functional Testing - 4 main points of difference

Functional Testing Tools

Functional testing is critical in the software development lifecycle, ensuring that the software behaves as expected and meets the specified requirements. Numerous functional testing tools have been developed to facilitate this process, each with unique features and strengths. This section explores some of the most popular and effective functional testing tools available to developers and testers.

1. Selenium

Selenium is an open-source automation testing tool widely used for web applications. It supports many programming languages, allowing testers to write test scripts in the most comfortable language. Selenium WebDriver, a component of Selenium, enables automated testing to be conducted on various web browsers. Its compatibility with numerous browsers and operating systems makes it a versatile choice for functional testing.

2. TestComplete

TestComplete is a comprehensive automation testing platform that supports desktop, mobile, and web applications. It offers a powerful interface that allows testers to create automated tests without deep programming knowledge. TestComplete supports various scripting languages, including JavaScript, Python, and VBScript, and provides advanced capabilities for recording, editing, and running tests. Its ability to sync with other tools and frameworks enhances its utility in a complex testing ecosystem.

3. QTP/UFT (Unified Functional Testing)

Developed by Micro Focus, UFT is a commercial functional and regression testing tool. It supports various web, desktop, and mobile applications and offers an intuitive visual interface that simplifies test creation and execution. UFT integrates seamlessly with other Micro Focus tools, providing a robust solution for continuous testing and integration.

4. JUnit and NUnit

JUnit and NUnit are frameworks used for unit testing in Java and .NET environments. While they are primarily designed for unit testing, they can also be used for functional testing by integrating them with other tools. These frameworks facilitate test-driven development (TDD) and behavior-driven development (BDD), promoting a more structured and efficient testing process.

5. Cucumber

Cucumber allows the specification of application behavior in plain language. This makes it easier for stakeholders, including those without technical backgrounds, to understand the tests. Cucumber supports various languages, including Ruby, Java, and .NET, and integrates with Selenium and other testing frameworks to facilitate comprehensive functional testing.

6. Postman

Postman helps with the functional testing of web services. It provides a user-friendly interface to send requests to web servers and analyze responses. Postman supports automated testing through scripting and collection runners, making it a valuable tool for testing the functionality of RESTful APIs and other web services.

Process Workflow for Functional Testing

The process workflow of a functional test includes three steps. They are: 

  1. Create input values
  2. Execute test cases
  3. Compare the actual output with the expected result.

Functional testing generally follows the steps mentioned below:

  1. Determine which aspect of the software system the testers need to test. These aspects or functionalities can vary from error conditions, product usability, messages, or central functions. 
  2. Create input data according to specific requirements for the functionalities that need testing.
  3. Based on the outlined requirements, determine which output parameters are acceptable and which ones are not.
  4. Execute test cases.
  5. Finally, compare the expected output with the actual result you receive from the test. Tracking this will reveal if your software system works well.

Example: Use Case Scenario for Functional Testing


Users log in to an Human Resource Management System (HRMS) portal with their login ID and password. The login page of the HRMS portal has two text fields –one for users to enter their username and the other for password–and two buttons – cancel and log in.

The action: The user enters their login credentials into the text fields.

The result: The user clicks on the login button and gets directed to the HRMS home page. The login gets canceled when the user clicks on the login button.


  1. User ID field: Users must enter a minimum of 6 characters and a maximum of 10. They can include numbers from 0-9, letters from A-Z, both upper and lower case, and can only contain a period, a hyphen, and an underscore for special characters. Users cannot leave any field blank. Their ID must begin with a number.
  2. Password field: Users must enter a minimum of 6 characters and a maximum of 8. The password must include numbers from 0-9, letters from A-Z, upper and lower cases, and special characters. Users cannot leave the password field blank.  

The above use case is a basic example of functional testing. Many functional testing techniques can help us to test it. Here are a few:

System Tests

The system test helps check all the system components and understand if they work perfectly together. In the above example, this would mean testing the customer journey from loading the HRMS app, the user entering proper credentials, getting redirected to the main page, the user performing tasks, and eventually logging out of the HRMS app. The test ensures that this entire journey is seamless and without any bugs.

Equivalence test

Segregation analysts segregate test data into partitions. These partitions are called equivalence data cases. The equivalence test checks to see if the data in each partition responds similarly. Therefore testing one condition across all partitions will give you the desired result. Since if the condition does not work in one, it will not work in any. In the above example, if the user enters characters > 10, the result must be the same.

Boundary Value Tests

Boundary value tests check the system's behavior when a user does not meet certain data limits. In the above example, the user must enter a password that requires a minimum of 6 characters. This test helps understand the system's response when the user enters a less than six characters password. 

Decision-based tests

The decision-based tests help understand how the system responds when the user meets a particular condition.

You can undertake the following decision-based tests in the above example:

  • When the user enters the wrong credentials, he should get an alert from the user and reload the page.
  • The system should take the user to the home page if he enters the correct credentials.
  • If the user cancels the login after entering the correct credentials, he should not get redirected to the home page but instead to the login page.

Ad-hoc Tests

Ad-hoc tests help uncover issues within the system software that you might not have identified through other tests. Ad-hoc tests break the system to check its response. In the above example, an administrator would run an ad-hoc test by deleting a user account while the user is performing tasks in his account. The test will help the administrator to understand if the system responds seamlessly in this situation.

Check out: Calculation of ROI in Mobile App Automation Testing

Advantages and Disadvantages of Functional Testing


  • This test reproduces the product in a live environment, and its focus is on the operating system, browsers, system specifications, and more. 
  • It does not work on hypotheticals and deals directly with the system's structure.
  • Organizations can deliver high-quality products through this testing methodology. It enables them to meet customer requirements and ensure customer satisfaction.
  • This test helps organizations deliver a bug-free product and one that meets all the customer's requirements.
  • Risk-based testing ensures a decrease in the chances of risk.


While this test ensures the product meets the customer requirements, it does not consider the performance, throughput time, responsiveness, and others. These aspects are essential to test for the overall health of the product. 

Additionally, functional testing fails to account for variables like the time it takes to execute specific functions, the security of the app, and other essential aspects. While functional testing is critical, it cannot certify if an application is ready for real-world use.


  • Many times testers can end up performing redundant tests.
  • Testers can miss out on logical errors present in the product.
  • Since testers run this test based on requirements, it can be time-consuming if the testing requirements are not precise or complicated.

Automated Functional Testing

Why Automate Functional Testing?

Automating functional tests helps improve efficiency. It lets you take simple tasks away from manual workers and give them to AI; this allows the company a chance to save money. It also helps save time as testers no longer have to run tests repeatedly, thus optimizing all your processes.

With automated functional testing, you will not have to worry about test efficiency as automation tools will ensure effective and efficient ways of testing. Automation processes are extensively scalable and don't require sourcing or paying new hires, making them an excellent investment. 

The aspect of scaling is vital for enterprises liable to rapid growth since they will need to invest in highly scalable solutions. Startups also must consider this since they have the prospect of moving from a small to a large scale business quickly. 

Benefits Of Automated Functional Testing

Automated functional testing has many benefits. Here are a few of them:

  • Automation affects the testing process: Automated functional testing helps speed up the testing process meaning developers will have more time to focus on bugs. With more time, the chances of developers addressing bugs through quick fixes will reduce. Quick fixes only address the superficial and do not fix the root cause. With faster testing processes in place, developers have all the time to address core concerns and solve issues. The HeadSpin platform provides actionable insights that your developers can use to their benefit. 
  • Automation lets you add several test cases: Manual testing can limit the use of test cases based on the capacity of the tester. However, the number of test cases you can add with automation is endless. Organizations can identify their needs and accordingly increase the test cases. 
  • Automation sticks to the timeline: Another reason automation is effective is that it sticks to the timeline. With automation meeting its timelines, developers can organize more tests, address issues, and continue to improve the app. 

Automation helps improve app quality: With automation in place, you have the means to run tests often. The more often you run tests, the better the quality of your final product. The increase in product quality will surely help your company grow.

Read: Appium Tools for Rapid Development of Functional & Performance Tests

What to Consider When Going for Automation

Automation Tool Selection

There are many automation tools you can choose from; however, the best way to select the one that works for you is by creating a list of requirements. Here's what you can add to the list.

  • The tool you select should be easy to use by all the members of the QA team.
  • Testers can use the tool across various environments. 
  • The automation functional testing tool should have all the features you need, like support for automated build tests, logging, specific reporting, and more.
  • The tool should support the reusability of test cases.

Here are some of the automation tools that you can choose from:

  • Appium
  • Selenium
  • QTP
  • Junit
  • SoapUI
  • TestComplete
Also read: Choosing a Test Automation Tool - A Complete Guide

Know which test cases need automation

Knowing which test cases you need to automate to get the best out of automation is essential. For example, manual testers are best for handling test cases that require adjustments in setup or configurations during test execution. Here are some that you can automate:

  • Tests that need to run repeatedly
  • Tests that run with various kinds of data
  • Error-prone tests
  • Tests that need to run in multiple browsers, and environments

Have a team dedicated to automation

Many organizations overlook this point and have all members of the QA team learn automation. 

While internal training is excellent, it is essential to understand that each member has different experience levels, interests, and skills. In such cases, it is good to understand each team member's skills and have selected members doing automation. A dedicated team of individuals with the right drive will focus on automation and bring out the best results.

If you’re looking for a way to do this, the HeadSpin University can help you. It offers courses on Appium and connects you with leaders in the test automation industry. A core Appium contributor, the project lead for the Appium Mobile Automation Platform, and the Director of Automation Technologies at HeadSpin, Jonathan Lipps, instructs students with walkthroughs on using automation and building apps.

Data-driven tests

Developers need to write automated test cases requiring multiple sets of data well. A well-written test case is reusable. They can write this data in configuration files or read them from a database. Creating a well-structured data source will make it easier for you to maintain the framework allowing you to use the test cases to their full potential. 

Changes to the UI should not affect your test cases

UI changes must not affect the test cases that you create. For example, earlier versions of Selenium identified page elements through a location. So a change in UI meant that those elements would suggest that you could no longer find those locations, leading to failed tests. Understanding the tool and writing test cases to ensure minimal changes to the UI will help.

Read: How Can You Prioritize Automated Functional Test Scenarios?

Test Frequently

Having an automation device pool ready is the first step. Ensuring that this bucket has frequent executions is the next; this helps in two ways; first, it enhances the test automation framework, and second, it enables you to catch more bugs.

Functional testing with HeadSpin

The HeadSpin Platform allows you to connect to real devices from around the world. You can run multiple tests in tandem. It integrates seamlessly with your CI/CD workflows, enabling functional testing both pre and post-release. 

Our machine learning provides detailed insights, automatically highlighting issues and pointing out the underlying root cause; this enables developers to get straight to the problem and fix it, thus significantly improving time to market.


Q1. Are functional testing and integration testing similar?

A1. Testers run functional tests to validate all functionalities of an application. On the other hand, integration testing ensures that modules, when compiled together, interact seamlessly and work well. 

Q2. What is defect severity?

A2. Defect severity highlights the impact of a defect on an app. Its severity depends on the defect's effect on the software's functionality. Defect severity is of four types:

  • Critical
  • Major
  • Medium
  • Low

Q3. Explain the difference between build and release


Build: Build is the executable file you give to a tester who uses this file to fix bugs and test the application's functionality. An app can have multiple builds. The testing team can reject the build if it does not pass the checklist.

Release: Release refers to the app no longer in the testing phase. The organization tests the app and gives it to the client. One release can have several builds.

A Complete Guide to Functional Testing

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