Software testing and the PABX

The topic of software testing is as general as the blue sky, and because software has become one of the key ingredients used to build machines, testing methodologies have become an important part of the overall software development cycle, particularly in highly demanding real time environments. A good software test insures that the machine performs in the manner envisioned by its creators. While testing can be done at many stages ranging from design and code reviews to low level testing of code at the procedure and subroutine level, the focus of this paper will be on testing the functional behavior of the end product. Testing of a special class of machine, the Private Automatic Branch Exchange, (PABX) is discussed along with a novel approach which was developed and successfully applied. The PABX can be characterized as a finite state machine, but for testing purposes it has an almost infinite number of states to test. This paper will discuss the selection and formalization of an algorithmic testing notation and set of related procedures which insures stringent product quality goals while at the same time reducing the testing effort to a reasonable and manageable task.