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Functional Testing Vs. Non-functional Testing: A Comparative Analysis

Functional Testing Vs. Non-functional Testing
Functional testing tells us 'what the system does', whereas non-functional testing gives us the answer to 'how well the system does.' Techspirited notes down the differences between functional and non-functional testing with examples.
Techspirited Staff
Last Updated: May 11, 2018
Functional testing is a type of black box testing, and not vice versa!
Functional testing determines the working of the system and ensures if it is being proposed as per the business specifications. It takes into consideration functions such as business processes, user commands, GUI interactions, data manipulation, user screens etc., and covers how well the system executes such functions. The ultimate goal is to check if the system is functionally perfect.
Non-functional testing is the type of testing done to check the readiness of the proposed system. This testing is done against the non-functional requirements like speed, scalability, performance, etc. These requirements reflect the quality of the product and gauge the final product by mapping it with the user's perspective. Non-functional testing can be executed only after the completion of functional testing.
Let's look at a brief comparison between functional and non-functional testing types.
Functional Vs. Non-functional Testing
Objective
  • To describe what the product does.
  • To describe how good the product works
Input
  • Functional testing is done in conformity with the business requirements.
  • Non-functional testing is conducted on performance parameters such as speed and scalability.
Flow
  • Functional testing is carried out first.
  • Non-functional testing takes place after functional testing is done.
Type of Testing
  • Both manual testing and automation testing tools are used for performing functional testing.
  • Manual testing is done with ease.
  • Automated tools are used for non-functional testing.
  • It is tedious to do manual testing when conducting non-functional testing.
Types
Prominent types of functional testing include:
  •  Smoke Testing
  • Sanity Testing
  • Regression Testing
  • Usability Testing
  • Unit Testing
  • Integration Testing
Types of non-functional testing include:
Performance Testing
Stress Testing
Security Testing
Installation Testing
Compatibility Testing
Load Testing
Volume Testing
Examples
  • Is the proposed system working as per the user requirement?
  • Is the GUI responsive? Is it easily accessible?
  • Does it perform basic functions as per requirement specifications?
  • How long does it take to log in?
  • How many people can log in at a time?
  • How efficiently the product works in different browsers?
Hence, the main difference is that a functional test would tell if your product has met customer requirements and checks for minor bugs; however, a non-functional test checks if it could stand up to a customer's expectations.