Compatibility testing is a non-functional software testing that helps evaluate a system/application's performance in connection with the operating environment.
Compatibility testing is one of the several types of software testing performed on a system that is built based on certain criteria and which has to perform specific functionality in an already existing setup/environment.
Compatibility of a system/application being developed with, for example, other systems/applications, OS, Network, decide many things such as use of the system/application in that environment, demand of the system/application, etc.
Many a time, users prefer not to opt for an application/system just because it is not compatible with any other system/application, network, hardware, or OS they are already using. This leads to a situation where the development efforts taken by developers prove to be in vain.
It is a type of testing used to ensure compatibility of the system/application/website built with various other objects such as other web browsers, hardware platforms, users (in case if it's very specific type of requirement, such as a user who speaks and can read only a particular language), operating systems, etc.
This type of testing helps find out how well a system performs in a particular environment that includes hardware, network, operating system, other software, etc. It can be automated using automation tools or can be performed manually and is a part of non-functional software testing.
Developers generally lookout for the evaluation of following elements in a computing environment (environment in which the newly developed system/application is tested and which has similar configuration as the actual environment in which the system/application is supposed to fit and start working).
Evaluation of the performance of system/application/website on a certain hardware platform. For example: If an all-platform compatible game is developed and is being tested for hardware compatibility, the developer may choose to test it for various combinations of chipsets (such as Intel, Macintosh GForce), motherboards etc.
Evaluation of the performance of system/website/application on a certain type of browser. For example: A website is tested for compatibility with browsers like Internet Explorer, Firefox etc. (usually browser compatibility testing is also looked at as a user experience testing, while using it on different browsers).
Evaluation of the performance of system/application/website on network with varying parameters such as bandwidth, variance in capacity and operating speed of underlying hardware etc., which is set up to replicate the actual operating environment.
Evaluation of the performance of system/application in connection with various systems/peripheral devices connected directly or via network. For example: printers, fax machines, telephone lines, etc.
Compatibility between versions
Evaluation of the performance of system/application in connection with its own predecessor/successor versions (backward and forward compatibility). For example: Windows 98 was developed with backward compatibility for Windows 95 etc.
Evaluation of the performance of system/application in connection with other software. For example: Software compatibility with operating tools for network, web servers, messaging tools etc.
Evaluation of the performance of system/application in connection with the underlying operating system on which it will be used.
Many applications/systems operate on databases. Database compatibility testing is used to evaluate an application/system's performance in connection to the database it will interact with.
How Helpful is It?
It can help developers understand the criteria that their system/application needs to attain and fulfill, in order to get accepted by intended users who are already using some OS, network, software and hardware, etc. It also helps the users to find out which system will better fit in the existing setup they are using.
The most important use of the compatibility testing is as already mentioned: to ensure its performance in a computing environment in which it is supposed to operate. This helps in figuring out necessary changes/modifications/additions required to make the system/application compatible with the computing environment.