Introduction

For more than 25 years there have been proposals for component-based approaches to software development [5]. However, only recently have off-the-shelf components become available commercially. Currently, software components in the form of C++ class libraries are available from hardware manufacturers such as IBM, and software development companies including Microsoft, Unix Systems Laboratories, and Rogue Wave Software.

From the tester's point of view, these libraries can be divided into two broad groups:

• Graphical User Interface (GUI) classes provide window and menu creation and manipulation, and keyboard and mouse event handling. GUI classes interact heavily with the environment through the keyboard, mouse, and screen.
• Collection classes provide object-oriented abstract data types: sets, lists, queues, trees, etc. With these classes, interaction is entirely through function calls and return values.

With object-oriented methods, productivity and reliability can be vastly improved, primarily through reuse. Because reliability depends on testing, this improvement cannot be realized without effective class testing. Our research focuses on the automated testing of collection classes [2,3].

There are two main requirements for class test suites:

• Effective. The tests must be likely to reveal faults if present. Generally, it is far more difficult to quantify test effectiveness for software than for hardware. As a minimal requirement, we generate tests that achieve 100% statement coverage of the code under test.
• Affordable. The test suite development and maintenance costs must be reasonable. As a rule of thumb, we seek test suites that cost significantly less to develop and maintain than the code under test.

To date there has been very little work in university or industry on class testing. This gap jeopardizes the future of object-oriented software engineering.