What are different characteristics of non-functional testing?

Non functional testing can be defined as the testing of the software system or the application for its all non functional requirements. It happens many times that the names of the non functional requirements get overlapped during the non functional testing.

Therefore, the name so the non functional requirements are used interchangeably many times. Non functional testing includes various testing aspects. Few have been given below:
- Compatibility testing
- Baseline testing
- Compliance testing
- Endurance testing
- Documentation testing
- Internationalization testing
- Localization testing
- Load testing
- Recovery testing
- Performance testing
- Security testing
- Resilience testing
- Scalability testing
- Usability testing
- Volume testing
- Stress testing

In non functional testing, typically the software system or the application is tested against the specifications and conditions listed by the client or the customer.
Non functional testing is entirely based upon the test cases and specifications and the requirements stated by the customer or the client.

Apart from the above listed non functional requirements aspects there are several other aspects covered by the non functional testing. They have been listed below:
- Ergonomics testing
- Migration testing
- Data conversion testing
- Penetration testing
- Installation testing
- Operational testing
- Readiness testing
- Application security testing
- Network security testing
- System security testing

Non functional testing is carried out only after the functional testing has been successfully completed on the software system. Earlier, non functional testing was not considered important. But, eventually software engineers started realizing its importance and they began to concentrate on the extra external feature of the whole software and the hardware system like reliability, interface testing and configuration testing. So, the non functional testing came to the scene and has got a great importance in the field of software development.

Comparison between functional and non-functional testing
- Functional testing gives coverage and concentrates on the relevant functionality or part of the software system or the application whereas non functional testing focuses primarily on the irrelevant components or functionality of the whole software system. The best example is given by graphical user interface or GUI which is also known as look and feel testing.

Generally non functional requirements include performance, volume, stress, load, and security, recovery etc and so on.

- Manual testing as an aspect of non functional testing relates to the testing of functionality which are simply not mentioned in the functional requirements documentation. This is how manual testing and non functional testing is related to each other.

- Functional testing relates to the business documents, requirements documents, test plans and exact mapping of the variables. Non functional testing is in great contrast with the functionality testing.

- Functional testing deals with the stability of the software system or the application. For example, it checks how the software system or the application responds to the irrelevant data input for some function. Non functional testing is a kind of ad hoc testing. But it also checks the stability.

Non functional testing tests the requirements of a software system that do not relate to the functionalities of the software system or application. These non functional requirements include fail over and recovery, social-ability, performance, stress, security and so on.

Non functional testing is to test the features and specifications and the stability of the software system which don’t correspond directly to the business related functionalities i.e., functional requirements, but are equally necessary.
In non functional testing you can look and feel the objects. For example, the installation testing.