e data flow analysers exist (Korel, 1985). The reviewers usually have check lists to remind them of the issues More often this kind of check is provided as an extra service of a which need to be considered. The author is given at the end of the compiler. review a list of faults found. The main difference between inspections and walk throughs lies 25.7.2 Unit testing by execution in the route taken through the item by the reviewers. In an inspec- tion, the item is considered line by line sequentially, beginning at In conventional unit testing the code module is compiled, loaded in the first line. In a walk through the reviewers may begin with test to the computer and set to run. Input data is supplied and the data, following the logic of the item as dictated by the way in which observed behaviour of the software is compared with the expected the test data would be processed. behaviour. A peer review is a special case of an inspection, in which the reviewers are drawn from the author's project team. A simpler form of inspection is desk checking. Here just one 25.7.2.1 'Top-down' and 'Bottom-up' testing person normally carries out the review and the review is informal. With desk checking the author is not called upon to explain his A software unit is a component of the system. It is generally not a work, there is no real interaction or discussion, and there is no self contained program and cannot be run alone. It may rely on other independent moderator. The process can be an economical way to components of the system. This means that the order of testing is find faults, but it tends to be less thorough than the more formal important. If the unit to be tested depends on others, then it is approaches. convenient if those units on which it depends have already been tested. Some systems are defined as a hierarchy of units, with a single top 25.7.1.2 Code auditing level module representing the complete program and calling on subordinate modules to carry out the main tasks. These in turn can There are tools which can auto