What Is Functional Testing? Definition, Importance, and Types

Functional Testing

Functional testing is the method of testing your application against determined sets of inputs or specifications to check if all its functionalities are functioning properly and generating expected outputs accordingly. This is an essential part of your entire software testing process as you may see your app working and generating some results but, it might not be producing the desired results.

In all our articles, we have always made our readers aware of the importance of software testing and its automated processes. You can easily understand how crucial it is to ensure that the numerous applications that are getting released every moment, must be thoroughly tested to provide the best quality experience to their users. Also, the tech world is adapting test automation and advanced AI-based automated testing tools like Preflight to engage their entire product teams in testing irrespective of their coding knowledge. That way they are presently capable of achieving significantly high test coverage that is improving every moment.

However, for now, if we just focus on functional testing, besides ensuring that your app’s features are properly functioning, these tests also take care that the system suits the business scenarios and fulfills the business objectives. So, let’s get into the depth of this vital form of testing.

What Is Functional Testing?

Functional testing is a form of software testing that ensures that an application as well as all of its functionalities are functioning as they should. These tests are performed using black box testing techniques. That means the testers performing functional tests have no knowledge of the internal system logic and just check if the app is generating expected outputs for a set of determined inputs. The results are recorded as only pass or fail.

Why Is Functional Testing Important?

As we mentioned before, an application can somehow run and you will normally see all its functionalities running but, it will not get success in the operations that it is supposed to perform. That means your users will see the application working but they will not get the proper results for the actions they perform or the inputs they provide. Hence, eventually, the bad reputation of the application that it does not produce proper outputs will cause the downfall of your business, and you will never want that to happen. That makes functional testing an extremely necessary part of your test suite.

Types of Functional Testing

Well, you may have already got the idea that functional testing is not just a simple form of testing. It is kind of a testing class that can have different types of approaches towards success. In our articles, we have already elaborated on a few highly important types that you will get to know again here. So, let’s check out some important types of functional tests.

Unit Testing

As the name suggests, these tests are concerned with testing units (the smallest parts) of an application. That means if the architecture of a huge application is broken into numerous small modules, each one of them is a unit, and a unit test is concerned with testing one such unit only. So, these tests can be the smallest tests to write and the quickest ones to execute. Each unit test checks if a unit produces the expected results when proper parameters are provided to it.

However, these tests may look small and take the least amount of time to get executed, but they have such a significant impact on the overall test suite, that they are treated as the base of the testing pyramid, or better to say, the starting point of the entire testing process. The test coverage of unit tests is another highly important aspect and it is expected to successfully cover the following -

  • Line coverage.
  • Code path coverage.
  • Method coverage.

Smoke Testing

This is another important type of functional test to check the critical parts of the application after the release of every build version. These tests are some kind of quick tests that check if the most critical parts of the application are working as they are supposed to. You are most likely to have a very smooth testing experience through these tests. Another important characteristic of these tests is that they test the application at a very basic level and make the way for you towards deciding that if the functionalities are failing at the basic level, it should not proceed towards the forward path for now, and should be sent back to the developers for review & correction.

Integration Testing

Integration tests come as the second phase of the testing pyramid and they truly have a justified position after the unit tests because when the unit tests have verified that the individual units are performing properly, they have to be tested for their combined functionality. That means integration tests verify that the planned combinations of the units are working correctly. These tests are extremely important because individual units may perform normally but when they are dependent on each other, if the integration among them is not seamless or has faults, the functionalities that the combinations of units have to perform may fail. That means integration tests are responsible for ensuring that the end-to-end outcome of the integrated units is up to the mark.

Sanity Testing

The name sanity testing is often taken just after the smoke testing and sometimes, they are also called cousins. That’s because sanity tests do almost the same things as smoke tests. They also test the critical functionalities at basic levels and if there are some issues, they prevent the application from moving towards further time-consuming tests that will eventually fail and cause the wastage of huge amounts of resources. However, the difference between smoke tests and sanity tests is that, unlike smoke tests, sanity tests are executed at a later stage in the process. They are performed to check if a new code change has the expected effect on the existing codebase. This similarity with a “sanity check” on proper performance of new code changes caused these tests to be called “sanity tests”.

Regression Testing

Now comes one of the most crucial forms of functional testing. Regression tests ensure that any new code change is not harming the existing functionalities of the application. So, the objective of these tests is to check if new code changes are not making the quality of the application “regress”, or in simple terms, go backward. That is why these tests are named “regression tests”. The purpose of performing these tests is to make sure whatever changes are being made to the code, the overall quality of the codebase as well as of the app remains stable and progressive.

UI/UX Testing

User Interface (UI) and User Experience (UX) are the portions that impress your users and attract more potential users to your app. The user interface represents the visual aspects that the users interact with. That means all the buttons, texts, forms, menus, images, etc. together make the user interface and how they perform, or what experience the users receive from the app is termed as user experience. Hence, it is highly important to perform detailed UI/UX tests to make sure that you provide your users with the best user interface as well as the best user experience. This type of testing is also called visual testing due to the point of action being the visual aspect of the application. Though these tests can sometimes be performed manually, using efficient automated testing tools is a profitable approach for your business.

User Acceptance Testing (UAT)/Beta Testing

These tests are somewhat real tests where the users test the product. In these tests, the application is exposed to a small group of real users who do not have any prior knowledge or experience with the application. Then they use the application in a production environment to find out how comfortable they are with the interface as well as the overall experience. It is also observed that if the application is solving the users’ requirements. This is a great testing approach as the users without any prior knowledge or experience about the application can find out unknown bugs that the technical professionals could not notice. The feedback of the users is then used for further quality assurance measures before the final launch of the product.

Benefits of Functional Testing

The amazing advantages that make functional testing so important for every tech business are mentioned below.

  • Being totally focused on the replica of the actual product, or testing it for the maximum convenience for the users, these tests pave the way for ensuring that all the functionalities of the application run suitably for the users. That means these tests take care of the factors like browsers, operating systems, system specifications, etc. that the users’ behavior depends on.
  • These tests produce results based on real users’ behavior. So, they ensure that the final product has remarkable quality and fulfills all the requirements of the end-users.
  • These tests run based only on proper parameters and do not rely on any if or but conditions or assumptions.
  • These tests work intending to produce a bug-free product that works as expected. So, you get to see nearly perfect test results.
  • It ensures the highest security and safety for the product.
  • These tests include risk-based tests that ensure that the product has minimal risks.

Limitations of Functional Testing

Now, like everything else or like every other tech product available in the market, functional testing also comes with a few limitations. These tests are performed with the goal to ensure that the product has the maximum quality and fulfills all the requirements of the users, but these tests do not take factors like the performance of the product i.e. responsiveness, etc. into account. Hence, that phenomenon causes a few limitations that you have to make plans to overcome are -

  • Being mostly focused on the functionalities of the application, these tests can miss out on a critical logical error in the codebase.
  • There are many chances of the tests being redundant.
  • These tests can not be treated as the final checkpoint for the product to go live.
  • These tests are mostly based on the requirements of the users. So, if somehow the requirements are not clear or complicated enough to not understand them, it becomes really difficult to perform the tests.


This article clearly shows you how important functional tests are. You may have an amazing app with a number of awesome features, but if those features fail to function properly, they will be of no use. Such a pathetic user experience will surely end up causing a bad impression as well as a disastrous consequence for your business.

However, you saw here how some basic types of tests can check those parameters minutely and ensure that all the features of your app are functioning properly and completing all the tasks they are supposed to perform. Those tests are cumulatively called functional tests. In this article, you also went through the benefits of performing these tests and figured out that they are an essential part of running a successful tech business. You also became familiar with the limitations of these tests to keep yourself prepared with the strategies to overcome those limitations and bring out the best results.

Performing functional tests is essential to successfully launch & run an efficient app, but the more important part is automating them. Manual testing becomes evidently less efficient and causes significant inaccuracies in most of the tests. Also, you have seen in all our articles and several other articles how efficient it becomes to automate the tests using advanced AI-based automated testing tools like Preflight. This simple browser extension can easily solve all your testing needs without involving you in even a little bit of coding. Hence, using this tool allows you to have your entire product team work collaboratively on the testing process regardless of their coding knowledge. And, the best part is that you can take a glance at that amazing testing experience for free.

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