System testing

System testing of software or hardware is testing performed on a complete, integrated system to check and evaluate the system's compliance with its specified requirements. System testing falls within the scope of black box testing, and as such, should require no knowledge of the inner design of the code or logic. [1]
As a rule, system testing takes, as its input, all of the "integrated" software components that have successfully passed integration testing and also the software system itself integrated with any applicable hardware system(s). System testing is a more limiting type of testing; it seeks to detect defects both within the "inter-assemblages" and also within the system as a whole.
Testing the whole system
System testing is performed on the entire system in the context of a Functional Requirement Specification(s) (FRS) and/or a System Requirement Specification (SRS). System testing is an investigatory testing phase, where the focus is to have almost a destructive attitude and tests not only the design, but also the behavior and even the believed expectations of the customer. It is also intended to test up to and beyond the bounds defined in the software/hardware requirements specification(s). System testing includes the Load testing and Stress Testing. Once the Load testing and Stress testing is completed successfully, the next level of Alpha Testing or Beta Testing will go ahead.
Types of system testing
The following examples are different types of testing that should be considered during System testing:
• GUI software testing
• Usability testing
• Performance testing
• Compatibility testing
• Error handling testing
• Load testing
• Volume testing
• Stress testing
• User help testing
• Security testing
• Scalability testing
• Capacity testing
• Sanity testing
• Smoke testing
• Exploratory testing
• Ad hoc testing
• Regression testing
• Reliability testing
• Recovery testing
• Installation testing
• Idempotency testing
• Maintenance testing
• Accessibility testing
(Source: Wikipedia.com)

I have experience performing system testing. I must admit that the job is a laborious one considering the fact that you have to test every niche of the site. But in the end I find it fun and very interesting. Some would disregard system testing and even say "Why test at all?". Why indeed? If your site provides services like online transaction, online buy and sell, etc. then you definitely need a polished, almost perfect and error-free site. If you did not perform a thorough system testing, there is a huge possibility that people will always encounter bugs, problems, etc. And if there are many dissatisfied customers, then they will not patronize your services. And if they will not patronize your services or will not visit your site anymore, then it will be a big financial loss to you. So my advise is, DO NOT FORGET TO SYSTEM TEST YOUR ENTIRE WEBSITE, SOFTWARE OR SOFTWARE/HARDWARE.
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Website QA/Tester