The Art of Software Testing, Second Edition

6.2. System Testing

System testing is the most misunderstood and most difficult testing process. System testing is not a process of testing the functions of the complete system or program, because this would be redundant with the process of function testing. As shown in Figure 6.3, system testing has a particular purpose: to compare the system or program to its original objectives. Given this purpose, two implications are as follows:

1. System testing is not limited to systems. If the product is a program, system testing is the process of attempting to demonstrate how the program, as a whole, does not meet its objectives.

2. System testing, by definition, is impossible if there is no set of written, measurable objectives for the product.

In looking for discrepancies between the program and its objectives, focus on translation errors made during the process of designing the external specification. This makes the system test a vital test process, because in terms of the product, the number of errors made, and the severity of those errors, this step in the development cycle usually is the most error prone.

It also implies that, unlike the function test, the external specification cannot be used as the basis for deriving the system test cases, since this would subvert the purpose of the system test. On the other hand, the objectives document cannot be used, by itself, to formulate test cases, since it does not, by definition, contain precise descriptions of the program's external interfaces. ...