The system test cases meant to test the system as per the requirements; end-to end. This is basically to make sure that the application works as per SRS. In system test cases, (generally in system testing itself), the testers are supposed to act as an end user. So, system test cases normally do concentrate on the functionality of the system, inputs are fed through the system and each and every check is performed using the system itself. Normally, the verifications done by checking the database tables directly or running programs manually are not encouraged in the system test.
The system test must focus on functional groups, rather than identifying the program units. When it comes to system testing, it is assume that the interfaces between the modules are working fine (integration passed).

 Ideally the test cases are nothing but a union of the functionality tested in the unit testing and the integration testing. Instead of testing the system inputs outputs through database or external programs, everything is tested through the system itself. For example, in a online shopping application, the catalog and administration screens (program units) would have been independently unit tested and the test results would be verified through the database. In system testing, the tester will mimic as an end user and hence checks the application through its output.

There are occasions, where some/many of the integration and unit test cases are repeated in system testing also; especially when the units are tested with test stubs before and not actually tested with other real modules, during system testing those cases will be performed again with real modules/data in