Functional vs Non-functional testing

Functional Testing

Testing the functionality of software based on requirements specification, a functional specification, or in use cases. It mainly involves black box testing where the functionality of any feature is tested by providing input(test data) and the output is compared with the expected results.

Testing of functionality is done from a requirements-based or business-process-based perspective. Requirements-based testing uses a specification of the functional requirements for the system as the basis for designing tests. Requirements are prioritized based on the risk criteria and this leads to prioritizing the tests. This will ensure that the most important and critical tests are included in the testing effort.

Business-process-based testing uses knowledge of the business processes where the scenarios involved in the day-to-day business use of the system are incorporated in the test cases. Experienced-based testing is also done as a part of functional testing. Test conditions and test cases are derived from the functionality of the component or system

Example of Functional Testing

1. Verify the user is able to login after entering correct credentials
2. Check if incorrect credentials are entered, the system should inform the user and reload the login page.
3. Check if the payment gateway throws an error when the incorrect card number is entered
4. Check if the add user screen successfully add the user in the system
5. Check if the future date or past date can be selected from a calendar
6. Check if the item added to the cart is displayed under view cart details

Types of Functional Testing

Non- Functional Testing

Testing the non-functional aspects of the software such as performance, security, reliability, usability, portability, etc. belongs to the category of non-functional testing. It is the testing of ‘how well’ the system works. Non-functional testing is equally important as functional testing as it affects client satisfaction. Quality not only depends on the functional aspects but also depends on Time, Accuracy, Stability, correctness, and durability of a product under various adverse circumstances. It is performed after functional testing.

Example of Non-functional Testing

1. Verify if the page load time should not be more than 5 secs when 1000 users accessing it simultaneously
2. Verify if the application works in different types of browsers
3. Check if the pages of the application are not directly accessible through URL without login.
4. Check if the document of size more than 2MB cannot be uploaded into the system

Types of Non-functional Testing

1. Performance Testing
2. Security Testing
3. Database Testing
4. Maintainability Testing
5. Usability Testing
6. Recovery Testing

 

Difference between Functional and Non-functional Testing

Functional Testing	Non- functional Testing
It focusses on testing the functionality of the software	It focusses on testing the non-functional aspects such as performance, security, usability, etc.
It revolves upon use cases	It revolves upon user expectation
It can be done manually or with the help of automation tool once the application is stable	It is hard to do manually and can be done with the help of a specialized tool
It starts from the initial stage of the software life cycle	It is done after functional testing is completed
It describes product features	It describes product properties
It is testing the application against business requirements	It is testing the application about client expectation and non- functional requirement
It tells how well the system is performing	It tells how well the system is responding
Product and Domain knowledge requires to perform functional testing	Architecture and design knowledge requires to perform non-functional testing
It is performed  during unit testing, integration testing, system testing, and acceptance testing level	It is performed only during system testing
It is mandatory to perform in all types of software	It is non-mandatory and performed based on the software needs