Introduction

An OO software system development is described which is meant to simulate the functionality of a VCR. The system is used to verify the high level design of the control program to be installed in the microcomputer unit of a new model VCR.

We focus on the behaviours required by the VCR user to derive the two scenarios.

The user triggers the Timer recording as follows: using the remote control, switch the TV on, press channel 1, press Video, press TV/VCR and press Menu; Menu appears on the TV monitor; set the timer as per the given instructions. The built-in timer must activate the VCR to record the program for the specified time interval. VCR's operation such as load, eject, play, record, pause, fastforward, rewind, and so on, and the TV Monitor's display and power are controlled by the hardware controllers and the remote controller (Navigator).

We use the Unified Modeling Language (UML) to describe our OO testing process. The VCR offers a number of functionalities such as timer recording, audio dubbing, and tape dubbing that can be treated as separate use cases. We rank timer recording as of the highest priority, and so, explore it as the first use case. We use the first use case diagram to explore system testing and to validate that the system behaves according to the definition in this diagram.

Fig 1. Use case diagram for the VCR system

The VCR system has a number of interacting objects such as the VCR, TV Monitor and a Remote Control (Navigator). In scenario 1 for setting timer details, the VCR system is required to simulate the remote control operations by setting the timer operations of the VCR. It uses the TV Monitor as the user interface medium while setting the timer details.

In scenario 2, we require the remote control object to control the VCR operations such as play, fast forward (ff), vol+ and others, and display the video pictures on the monitor. We also require the monitor surface for visualizing the state diagram that shows the interaction between VCR & Monitor objects.

Interaction diagrams in UML are scenario models that describe the collaborative behaviour of groups of objects. An interaction diagram usually captures the behaviour of a single use case, and is used to show the objects, and message passing between objects.

We have chosen to discuss test selection techniques for system level testing for scenario 1, and unit level and integration level testing for scenario 2. Integration tests use collaborative diagrams and sequence diagrams to validate the interactions between objects.