Software Engineering For Students: A Programming Approach Part 42. This fully revised version of Doug Bell's Software Engineering: A Programming Approach continues to use the successful formula of the previous editions. The author's approach is to present the main principles, techniques and tools used in software engineering, one by one, chapter by chapter. This book is a unique introduction to software engineering for all students of computer science and its related disciplines. It is also ideal for practitioners wishing to remain current with new developments in the area | 388 Chapter 31 Assessing methods In the experiment 59 people were asked to test a 63-line PL 1 program. The people were workers in the computer industry most of whom were programmers with an average of 11 years experience in computing. They were told of a suspicion that the program was not perfect and asked to test the program until they felt that they had found all the errors if any . An error meant a discrepancy between the program and the specification. The people were provided with the program specification the program listing a computer to run the program on and as much time as they wanted. Different groups used different verification methods. While the people were experienced and the program was quite small their performance was surprisingly bad. The mean number of bugs found was . The most errors any individual found were 9. The least any person found was 3. The actual number of bugs was 15. There were 4 bugs that no one found. The overwhelming conclusion must be that people are not very effective at carrying out verification whichever technique they use. Additional findings from this study were that the people were not careful enough in comparing the actual output from the program with the expected outcome. Bugs that were actually revealed were missed in this way. Also the people spent too long on testing the normal conditions that the program had to encounter rather than testing special cases and invalid input situations. The evidence from this and other experiments suggests that inspections are a very effective way of finding errors. In fact inspections are at least as good a way of identifying bugs as actually running the program doing testing . So if you had to choose one method for verification it would have to be inspection. Studies show that black box testing and white box testing are roughly equally effective. However evidence suggests that the different verification techniques tend to discover different errors. Therefore the more techniques that
