Functional Testing |What is, Process, Types, & Examples

Functional testing is a quality assurance process and a type of black-box testing that bases its test cases on the specifications of the software component under test. Functions are tested by feeding them input and examining the output, and internal program structure is rarely considered

FUNCTIONAL TESTING is a type of software testing whereby the system is tested against the functional requirements/specifications.
Functions (or features) are tested by feeding them input and examining the output. Functional testing ensures that the requirements are properly satisfied by the application. This type of testing is not concerned with how processing occurs, but rather, with the results of processing. It simulates actual system usage but does not make any system structure assumptions.
During functional testing, Black Box Testing technique is used in which the internal logic of the system being tested is not known to the tester.
Functional testing is normally performed during the levels of System Testing and Acceptance Testing.
Image result for functional testing
Typically, functional testing involves the following steps:
  • Identify functions that the software is expected to perform.
  • Create input data based on the function’s specifications.
  • Determine the output based on the function’s specifications.
  • Execute the test case.
  • Compare the actual and expected outputs.
Functional testing is more effective when the test conditions are created directly from user/business requirements. When test conditions are created from the system documentation (system requirements/ design documents), the defects in that documentation will not be detected through testing and this may be the cause of end-users’ wrath when they finally use the software.

What is Functional Testing: A Complete Guide with Types and Examples

Functional Testing Tutorial with Functional Testing Types and Examples:
Definition: As the name explains, a functional test is a kind of black box testing that is performed to confirm that the functionality of an application or system is behaving as expected.
Functional testing is done to verify all the functionality of a product. 


There must be something that defines what is an acceptable behavior and what is not.
This is specified in a functional or requirement specification. It is a document that describes what a user is permitted to do so that he can determine the conformance of the application or system to it. Additionally, sometimes this could also entail actual business side scenarios to be validated.
Therefore, functionality testing can be carried out via two popular techniques:
  • Testing based on Requirements: Contains all the functional specifications which form a basis for all the tests to be conducted.
  • Testing based on Business scenarios: Contains the information about how the system will be perceived from a business process perspective.
Testing and Quality Assurance are a huge part of the SDLC process.
As a tester, we need to be well aware of all types of testing even if we’re not directly involved with them on a daily basis.
As testing is an ocean, the scope of it is so vast, we have dedicated testers who perform different kinds of testing. Most probably all of us must be familiar with most of the concepts, but it wouldn’t hurt to organize it all here.
So let’s get back to some basics.

Testing Classes

Widely classifying, there are two kinds or classes of testing.
Testing classes

#1) Black Box Testing:

Black Box testing Technique is exactly what it sounds like! Picture a black colored box as shown below.
Black box testing
Let’s ask some basic questions to ourselves to derive a technical definition.
  1. Can you see the box’s external characteristics?
  2. Can you see what lies within the box?
If you now try to answer these fundamental questions, it’ll give you a perfect idea of what this entails. The answer to the above question is yes and no respectively. Therefore, black box testing can be defined as the type of testing where you view the system under test as a black box and observe how it reacts to various situations.
You don’t need to get into the system’s internal factors like its implementation, code or internal characteristics. The tester will derive the different inputs to this system based on the requirements, record the outputs for each of them and makes sure that they are consistent with the expectations.
Examples of Black box testing are: Functional testing (How it is affected by Cloud Automation), System testing, Acceptance testing, Regression testing, Beta testing and sometimes Integration testing also comes under this category.

#2) White Box Testing:

White box testing technique, on the other hand, is almost the opposite of the black box testing. Let us assume that the same black box is a transparent box as shown below.
White box testing
Again let’s ask some questions to derive its meaning:
  1. Can you see the box’s internal characteristics?
  2. Should you be testing the code?
The answer to both these questions is an affirmative “yes”. Commonly known synonyms for white box testing are glass box testing, transparent box testing, or structural testing.
Therefore white box testing is a mechanism where a tester has access to the internal code of the system and executes tests to check the robustness of the code. He doesn’t have to get into the actual functionality of the application.
Examples of white box testing include Unit testing, API testing, Integration and Regression testing also extends into this category based on scope. Sometimes even functional tests require the usage of white box testing.
Having formed a basis and background, now the scope of this article will be to discuss the functionality testing aspect in detail.

Functional Testing Types

It has many categories and these can be used based on the scenario.
The most prominent types are discussed below in brief:
  • Unit Testing: Unit testing is usually performed by the developer who writes different code units that could be related or unrelated to achieve a particular functionality.
Therefore, this usually entails writing unit tests which would call the methods in each unit and validate that when the needed parameters are passed, its return value is as expected. Code coverage is an important part of unit testing where test cases need to exist to cover the below three:
i) Line coverage
ii) Code path coverage
iii) Method coverage
  • Sanity TestingTesting that is done to ensure that all the major and vital functionalities of the application/system are working correctly. This is generally done after a smoke test.
  • Smoke testingTesting that is done after each build is released to test in order to ensure build stability. It’s also called build verification testing.
  • Regression testsTesting performed to ensure that adding a new code, enhancements, fixing of bugs is not breaking the existing functionality or cause instability and still works according to the specifications. Regression tests need not be as extensive as the actual functional tests but should ensure just the amount of coverage to certify that the functionality is stable.
  • Integration testsWhen the system relies on multiple functional modules that might individually work perfectly, but have to work coherently when clubbed together to achieve an end to end scenario, validation of such scenarios is called Integration testing.
  • Beta/Usability testingProduct is exposed to the actual customer in a production like an environment and they test the product. The user’s comfort is derived from this and the feedback is taken. This is similar to User Acceptance testing.
I’m again going to represent this in an easy flow-chart:
flow chart
Functional System Testing:
System testing is a testing that is performed on a complete system to verify that if it works as expected once all the modules or components are integrated. End to end testing is performed to verify the functionality of the product. This testing is performed only when system integration testing is complete including both the functional & non-functional requirements.

Difference Between Unit, Functional and Integration Testing

Tests a program by separating it into code modules or units and individually testing those modules.Tests a user scenario which involves two or more individual modules to work correctlyFunctional tests determine if the application is behaving according to specifications
Not very complex in natureMore complex than unit tests.More complex than unit tests and sometimes even more complex than integration tests.
It is a white box testing techniqueIt is a white box and black box testing techniqueIt is a black box testing technique
Unit testing helps in screening/uncovering bugs that might occur frequentlyIntegration testing will help uncovering the error that occurs when individual modules are assembled to work together.Functional testing helps to uncover bugs that do not let the application serve its desired purpose.
Unit tests should be more in numberIntegration tests should be added if it’s not possible to add a unit test as they are complex and take more time to executeFunctional tests should be less in number when compared to unit tests as they might take more time to execute.

Functional Test Process

The process has three main steps:
Functional testing Process
Approach, Techniques, and Examples
Functional or behavioral testing generates an output based on the given inputs and determines if the System is functioning correctly as per the specifications.
So the pictorial representation will look as shown below:
Functional Testing Process

Entry/Exit criteria

Entry criteria:

  • Requirement Specification document is defined and approved.
  • Test Cases have been prepared.
  • Test data has been created.
  • The environment for testing is ready, all the tools that are required are available and ready.
  • Complete or partial Application is developed and unit tested and is ready for testing.

Exit Criteria:

  • Execution of all the functional test cases has been completed.
  • No critical or P1, P2 bugs are open.
  • Reported bugs have been acknowledged.

Steps Involved

The various steps involved in this testing are stated below:
  • The very first step involved in Functional testing is to determine the functionality of the product that needs to be tested which includes testing the main functionalities, error condition and messages, usability testing i.e. whether the product is user-friendly or not etc.
  • Next step is to create the input data for the functionality to be tested as per the requirement specification.
  • Then from the requirement specification, the output is determined for the functionality under test.
  • Prepared test cases are executed.
  • Actual output i.e. the output after executing the test case and expected output (determined from requirement specification) are compared to find whether the functionality is working as expected or not.


Different kind of scenarios can be thought of and authored in the form of “test cases”. As QA folks, we all know how the skeleton of a test case looks.
It has mostly four parts to it:
  • Test summary
  • Pre-requisites
  • Test Steps and
  • Expected results.
Obviously, attempting to author each and every kind of test is not only impossible but also time-consuming and expensive.
Typically, we would want to uncover maximum bugs without any escapes with existing tests. Therefore, the QA needs to use optimization techniques and strategize how they would approach the testing.
Let’s explain this with an Example.
Functional Testing Example Use Case: 
Take an online HRMS portal where the employee logs in with his user account and password. On the login page, there are two text fields for the user, password, and two buttons: Login and Cancel. Successful login takes the user to the HRMS home page and cancel will cancel the login.
Specifications are as given below:
#1 ) The user id field takes a minimum of 6 characters, a maximum of 10 characters, numbers(0-9), letters(a-z, A-z), special characters (only underscore, period, hyphen allowed) and cannot be left blank. User id must begin with a character or number and not special characters.
#2) Password field takes a minimum of 6 characters, a maximum of 8 characters, numbers (0-9), letters (a-z, A-Z), special characters (all) and cannot be blank.
Example Use Case
The basic approach to testing this scenario can be classified into two broad categories:
  1. Positive testing and
  2. Negative testing
Of course, each of these categories has their own subsection of tests that will be carried out.
Positive tests are happy path tests which are done to ensure that the product means – at least the basic requirements that are vital to customer usage.
Negative scenarios ensure that the product behaves properly even when subjected to unexpected data.
Now let me try to structure the testing techniques using a flowchart below. We’ll get into the details of each of those tests.

Testing Techniques

Testing Techniques

#1) End-user based/System Tests:

The system under test may have many components which when coupled together achieve the user scenario.
In the Example, a customer scenario would include HRMS application loading, entering the correct credentials, going to the home page, performing some actions and logging out of the system. This particular flow has to work without any errors for a basic business scenario.
Some samples are given below:
Sl NoSummaryPre-requisiteTest caseExpected results.
1.Fully privileged user can make account changes1)User account must exist
2) User needs to have the required privileges
1) User enters the userid and password
2) User sees edit permissions to modify account itself
3) User modifies account information and saves.
4) User logs out.
1) User is logged into the home page
2) Edit screen is presented to the user.

3) Account information is saved
4) User is taken back to login page
2.Another valid user without full privileges1)User account must exist
2) User needs to have the minimum privileges
1) User enters the userid and password
2) User sees edit permissions to modify only certain fields.
3) User modifies only those fields and saves.
4) User logs out.
1) User is logged into the home page
2) Edit screen is presented to the user only on certain fields. The account fields are grayed out.
3) Fields modified are saved
4) User is taken back to login page
This is a basic example of how test cases are authored for situations. The format above will apply to all the below tests as well. For the sake of strong conceptual grounding, I have put in only some simple tests above and below.

#2) Equivalence Tests:

In Equivalence partitioning, the test data are segregated into various partitions called equivalence data classes. Data in each partition must behave the same way therefore only one condition needs to be tested. Similarly, if one condition in a partition doesn’t work, then none of the others will work.
For Example, in the above scenario the user id field can have a maximum of 10 characters, so entering data > 10 should behave the same way.

#3) Boundary Value Tests:

Boundary tests imply data limits to the application and validate how it behaves.
Therefore, if the inputs are supplied beyond the boundary values, it is considered to be negative testing. So a minimum of 6 characters for the user sets the boundary limit. Tests are written to have user id < 6 characters are boundary analysis tests.

#4) Decision-based Tests:

Decision-based tests are centered around the ideology of the possible outcomes of the system when a particular condition is met.
In the scenario given above, the following decision-based tests can be immediately derived:
  1. If the wrong credentials are entered, it should indicate that to the user and reload the login page.
  2. If the user enters the correct credentials, it should take the user to the next UI.
  3. If the user enters the correct credentials but wishes to cancel login, it should not take the user to the next UI and reload the login page.

#5) Alternate Flow Tests:

Alternate path tests are basically run to validate all the possible ways that exist, other than the main flow to accomplish a function.

#6) Ad-hoc Tests:

When most of the bugs are uncovered through the above techniques, ad-hoc tests are a great way to uncover any discrepancies not observed earlier. These are performed with the mindset of breaking the system and see if it responds gracefully.
For Example, a sample test case would be:
  • A user is logged in, but the admin deletes the user account while he is performing some operations. It would be interesting to see how the application handles this gracefully.

Functional vs Non-Functional Testing

Now, we had a detailed discussion about the functionality test. Let’s also briefly discuss the non-functional testing concept.
Non-functional tests focus on the quality of the application/system as a whole. So it tries to deduce how well the system performs as per the customer requirements as in contrast to the function it performs.
Non-functional test types: Some more popular kinds of non-functional tests are:
  • Performance: Stress, Load Testing: This testing is done to see if the application can withstand heavy stress and load when there are too many simultaneous users accessing the system at the same time.
  • Security testing: Testing which is done to determine how robust the application is to malicious attacks or unwarranted users.
  • Compatibility Testing: Testing is carried out to determine how well the application works in any particular environment.
  • Install Testing: Testing carried out to determine that the application can be downloaded, installed from something called a “package” and setup without any issues.
  • Recovery Testing: Testing done to figure out if an application is able to gracefully recover from disasters and catastrophic events such as hardware failures, system crashes, etc,
  • Volume/Tenacity Testing: Tests which are done to determine the application’s ability to handle a certain amount of data.
Below points specify the difference between these:
S.NO.Functional TestingNon functional testing
1Based on customer’s requirement.Based on customer’s expectation.
2Checks functionality of the applicationChecks the Performance i.e. responsiveness, throughput time etc of the application.
3Functional testing includes:
• Unit testing
• Integration testing
• System testing
• Sanity testing
• Smoke testing
• Interface testing
• Regression testing
• Beta/Acceptance testing
Non functional testing includes:
• Performance Testing
• Load testing
• Stress testing
• Volume testing
• Security testing
• Compatibility testing
• Install testing
• Recovery testing
• Reliability testing
• Usability testing
• Compliance testing
• Localization testing
4Functional testing is basically what an application does.Non- functional testing is how the application works.
5Manual testing is easy to perform in functional testing.Non-functional testing is not easy for manual testing. Most of it cannot be performed.
6Example: If an email is sent to customer on clicking submit button, then in functional testing correct email is sent to customer has to be verified.Email should be sent in 15 minutes – has to be verified in non-functional testing.

Functional & Non-Functional Requirements

Functional Requirements define what the system is supposed to do and what it will provide to the end user. It describes the functionality or behavior of the system.
Non- functional requirements define how the system will work for the performance of the system. It considers the constraints, quality factors which may hamper the functionality’s performance or their effectiveness. Non – functional requirement includes accessibility, efficiency, effectiveness, response time, throughput, reliability etc

Is User Acceptance Test Functional or Non-Functional?

User Acceptance test is performed by the customer to accept the product if it is as per their requirement and expectation.
While testing the product functionality of a product, it is verified if it is working as expected or not and this comes under functionality testing. Besides that, the performance of the application i.e. the speed, response time, throughput etc., which comes under non-functional testing can also be tested.
So, basically, UAT cannot be defined as functional or non-functional testing alone. As it’s an acceptance test in which the customer can choose to test what he/she requires to give a Go live approval.

Non-Functional Test Types

The various types of Non-functional tests are explained below:

#1) Reliability Testing:

Reliability testing, as the name itself suggests, is to make sure if the system is reliable and bug-free.
This testing is done in a specific environment for a specific time period and makes sure that the application works as expected and is bug-free. The main objective of Reliability testing is to find the number of failures in the defined span of time and the root cause of that failure.

#2) Localization Testing:

Localization testing is performed to verify that if the application is as per the locale i.e. as required in the language and country. Localization focuses more on the content of the application and the user interface. This testing covers testing the usability of UI, linguistic errors, typographical errors etc.

#3) Usability Testing:

Usability testing checks whether the developed application is user-friendly or not. It verifies the display screens, messages, navigation etc. Usability testing checks the user interface to see if it meets all the user requirements.

#4) Compliance Testing:

Compliance testing verifies if the developed software has followed all the specified standards for the product or not.

Automated Functional Testing

Can this Testing be Automated?
Automation is done so that manual effort can be reduced, time can be saved, bug slippage can be avoided, and efficiency can be increased. But it is not possible to automate each and everything. This testing can be automated but the user needs to work out for test cases for the automation to be done.
It’s important to find the right test cases to be automated along with the appropriate tool.
Automating functional testing can have drawbacks like if the number of test cases are much more and are regressed again and again ( which has to be done ) then the developer might face an issue in committing changes to the code.
Many times while performing defect escape analysis, the prominent and perennial cause of escapes seem to be a lack of test coverage in a particular function. Again, there are several causes for this to happen like lack of environments, lack of testers, too many functions being delivered, less time to cover all testing aspects and sometimes simply overlooking it.
While dedicated test teams might do detailed testing on each sprint or each test cycle, there will always be defects and there will always be defects that might get missed. This is one of the fundamental needs to have test automation in place, thereby having a marked improvement in efficiency of the overall test process and test cases coverage.
Although automated functional testing can never replace manual tests, having an ideal mix of the two will prove to be vital to have the desired quality in Software projects.
Automation Considerations:
#1) Select the correct Automation Tool: The number of tools available in the market, make the choice of the automation tool a real daunting task! However, you could make a list of requirements, based on which you can select what automation tool to use.
Some primary aspects to think of are:
  • Select a tool that will be easy to use by all the QA members of the team, if they don’t already have the needed skills.
  • The tool can be used across different environments For Example: Can the scripts be created on one OS platform and run on another? Do you require CLI automation, UI automation, mobile application automation or all?
  • The tool must have all the features you require. For Example: If some testers are not well-versed with a scripting language, the tool should have a record and playback feature and then support conversion of the recorded script to the desired scripting language. Likewise, if you need the tool to also support automated build tests, specific reporting, and logging, it must be able to do that as well.
  • The tool must be able to support reusability of test cases in case of UI changes.
Automation Tools: There are quite a few tools which are available for functional automation. Selenium is probably a hot favorite, but there are some other open source tools as well like Sahi, Watir, Robotium, AutoIt etc.
There are several functional testing tools that are available in the market. But choosing the appropriate tool is very important for the organization. It might depend on the requirement, ease of using and moreover, cost plays a major role.
Given below are few functional tools:
  • Selenium
  • QTP
  • Junit
  • Loadrunner
  • SoapUI
  • TestComplete
=> Check the below link for more details on the above tools and other functional tools.
#2) Pick the right test cases to automate: If you want to get the best out of automation, then it is vital to be smart about the kind of tests you pick to automate. If there are tests that require some setup and configurations on and off during test execution, those are best left non-automated.
Therefore, you can automate tests which:
  • Need to be run repeatedly.
  • Run with different kinds of data.
  • Some P1, P2 test cases which take a lot of effort and time.
  • Tests which are error-prone.
  • Set of tests that need to be run in different environments, browsers, etc.
#3) Dedicated Automation Team: This is probably overlooked in most organizations and automation is imposed upon all the members of the QA team.
Each team member has varying experience levels, skill sets, interest levels, bandwidth to support automation. Some individuals are possibly better skilled at executing manual tests, while some others may have the knowledge of scripting and automation tools.
In situations like this, it’s a good practice to take an analysis of all the members of the team and have some members dedicated to doing only automation. Automation activity requires time, effort, knowledge and a dedicated team which will help to achieve the required results instead of overloading all the members of the team with both manual and automation testing.
#4) Data Driven tests: Automated test cases that require multiple sets of data should be well written so that they can be reusable. The data could be written in sources such as text or properties file, XML files or read from a database.
Whatever the data source is, creating well-structured automation data makes the framework easier to maintain and makes the existing test scripts used to their full potential.
#5) UI changes must not break tests: The test cases you create using the selected tool must be able to deal with potential UI changes. For instance, earlier versions of selenium used a location to identify page elements. So if the UI changed, those elements were no longer found at those locations will lead to mass failure of tests.
Therefore, it’s important to understand the shortcomings of the tool beforehand and author test cases such that there are only minimal changes required in case of UI changes.
#6) Frequent testing: Once you have a basic automation test bucket ready, plan to have more frequent execution of this bucket. This has a two-way advantage: one is that you can enhance the automation framework and make it more robust; second is that you will obviously catch more bugs in the process.


There are several advantages:
  • This testing reproduces or is a replica of what the actual system is is a replica of what the product is in the live environment. Testing is focused on the specifications as per the customer usage i.e. System specifications, Operating system, browsers etc.
  • It does not work on any if and buts or any assumptions about the structure of the system.
  • This testing ensures to deliver a high-quality product which meets the customer requirement and makes sure that the customer is satisfied with the end results.
  • It ensures to deliver a bug-free product which has all the functionalities working as per the customer requirement.
  • Risk-based testing is done to decrease the chances of any kind of risk in the product.


This testing is done to make sure that the product works as expected and the entire requirement is implemented and the product is exactly as per the customer requirement.
But it does not consider the other factors such as the performance of the product i.e. responsiveness, throughput time etc., which are important and very much required to be a part of testing before releasing the product.
  • There are many chances of performing redundant testing.
  • Logical errors can be missed out in the product.
  • This testing is based on the requirement, if in case the requirement is not complete or is complicated or is not clear, performing this testing in such a scenario becomes difficult and can be time-consuming too.
So, basically functional testing alone is not sufficient to deliver a quality product. Non-functional testing also needs to be performed to deliver a high-quality product.


This tutorial has comprehensively discussed everything that you need to know about functional testing, right from the basics.
Functional testing is one of the important testing processes as it verifies the functionality of a product which is the most required and important aspect of any product or application.
About the Author: Sanjay Zalavadia – as the VP of Client Service for Zephyr, Sanjay brings over 15 years of leadership experience in IT and Technical Support Services. 
I hope that some of the techniques that we’ve suggested come in handy for all readers. Let us know your thoughts in the comments below.