System-level testing must be conducted prior to installation of an information system. It involves:
a) Preparation of realistic test data in accordance with the system test plan.
b) Processing the test data using the new equipment.
c) Thorough checking of the results of all system tests, and
d) Reviewing the results with future users, operators and support personnel.
System level testing is an excellent time for training employees in the operation of the IS as well as maintaining it. Typically, it requires 25 to 35 percent of the total implementation effort.
One of the most effective ways to perform system-level testing is to perform parallel operations with the existing system. Parallel operations consist of feeding both systems the same input data and comparing data files and output results. Despite the fact that the individual programs were tested, related conditions and combinations of conditions that were not envisioned are likely to occur. Last minute changes to computer programs are necessary to accommodate these new conditions.
For an interactive information system project, the process of running dual operations for both new and old system is more difficult than it is for a batch processing system, because the new system has no true counterpart in the old system. One procedure for testing the new interactive system is to have several remote input terminals connected on line are operated supervisory personnel backed up other personnel operating on the old system. The outputs are checked for compatibility, and appropriate corrections are made to the on-line computer programs. Once this segment of the new system has proved satisfactory, the entire terminal network can be placed into operation for this one work. Additional sections of the system can be added testing in this manner until all programs are operational.
During parallel operations, the mistakes detected are often not those of the new system, but of the old. These differences should be reconciled as far as it is feasible economically. Those responsible for comparing the two systems should clearly establish that the remaining deficiencies are caused the old system. A poor checking job at this point can result in complaints later from customers, top management, salespersons, and others. Again, it is the responsibility of the system developers and analysts to satisfy themselves that adequate time for dual operation has been undertaken for each functional area changed.