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System Testing

Testing is the major quality control measure employed during software development. Its basic function is to detect errors in the software. During requirement analysis and design, the output is a document that is usually textual and non-executable. After the coding phase, computer programs are available that can be executed for testing phases. This implies that testing not only has to uncover errors introduced during coding, but also errors introduced during the previous phases. Thus, the goal of testing is to uncover requirement, design or coding errors in the programs.

Consequently, different levels of testing are employed. The starting point of testing is unit testing. In this a module is tested separately and is often performed by the coder himself simultaneously with the coding of the module. The purpose is to execute the different parts of the module code to detect coding errors. After this the modules are gradually integrated into subsystem, which are then integrated themselves eventually form the entire system. During integration of modules, integration testing is performed. The goal of this testing is to detect design errors, while focusing on testing the interconnection between modules. After the system is put together, system testing is performed. Here the system is tested against tech system requirements to see if all the requirements are met and the system performs as specified by the requirements. Finally, acceptance testing is performed to demonstrate to the client, on the real life data of the client, the separation of the system.

For testing to be successful, proper selection of test cases is essential. There are two different approaches to selecting test cases-functional testing and structural testing. In functional testing the software for the module to be tested is treated as black box, and then test cases are decided based on the specifications of the system or module. For this reason, this form of testing is also called "black box testing". The focus is on testing the external behavior of the system. In structural testing the test cases are decided based on the logic of the module to be tested. Structural testing is sometimes called "glass box testing". Structural testing is used for lower levels of testing and functional testing is used for higher levels.

Testing is an extremely critical and time-consuming activity. It requires proper planning of the overall testing process. Frequently the testing process starts with the test plan. This plan identifies all the testing related activities that must be performed and specifies the schedule, allocates the resources, and specify guidelines for testing. The test plan specifies manner in which the modules will integrate together. Then for different test units, a test case specification document is produced, which lists all the different test cases, together with the expected outputs, that will be used for testing. During the testing of the unit, the specified test cases are executed and actual result is compared with the expected output. The final output of the testing phases is to the text report and the error report, or set of such reports (one of each unit is tested). Each test report contains the set of such test cases and the result of executing the code with these test cases The error report describes the errors encountered and action taken to remove those errors.

System testing is explained further in the chapter entitled "Testing and Quality Assurance"

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