Static test techniques provide a powerful way to improve the quality and productivity of software development. This chapter describes static test techniques, including reviews, and provides an overview of how they are conducted. The fundamental objective of static testing is to improve the quality of software work products by assisting engineers to recognize and fix their own defects early in the software development process. While static testing techniques will not solve all the problems, they are enormously effective. Static techniques can improve both quality and productivity by impressive factors.
Static testing is not magic and it should not be considered a replacement for dynamic testing, but all software organizations should consider using reviews in all major aspects of their work including requirements, design, implementation, testing, and maintenance. Static analysis tools implement automated checks, e.g. on code.
3.1 REVIEWS AND THE TEST PROCESS
- Recognize software work products that can be examined by different static techniques. (K1)
- Describe the importance and value of considering static techniques for the assessment of software work products. (K2)
- Explain the difference between static and dynamic techniques. (K2)
In Chapter 1, several testing terms were presented. Also testing itself was defined. The latter definition is repeated here as a means for explaining the two major types of testing.
The definition of testing outlines objectives that relate to evaluation, revealing defects and quality. As indicated in the definition two approaches can be used to achieve these objectives, static testing and dynamic testing.
With dynamic testing methods, software is executed using a set of input values and its output is then examined and compared to what is expected. During static testing, software work products are examined manually, or with a set of tools, but not executed. As a consequence, dynamic testing can only be applied to software code. Dynamic execution is applied as a technique to detect defects and to determine quality attributes of the code. This testing option is not applicable for the majority of the software work products. Among the questions that arise are: How can we evaluate or analyze a requirements document, a design document, a test plan, or a user manual? How can we effectively pre-examine the source code before execution? One powerful technique that can be used is static testing, e.g., reviews. In principle all software work products can be tested using review techniques.
Dynamic testing and static testing are complementary methods, as they tend to find different types of defects effectively and efficiently. Types of defects that are easier to find during static testing are: deviations from standards, missing requirements, design defects, non-maintainable code and inconsistent interface specifications. Note that in contrast to dynamic testing, static testing finds defects rather than failures.
In addition to finding defects, the objectives of reviews are often also informational, communicational and educational, whereby participants learn about the content of software work products to help them understand the role of their own work and to plan for future stages of development.
Reviews often represent project milestones and support the establishment of a baseline for a software product. The type and quantity of defects found during reviews can also help testers focus their testing and select effective classes of tests. In some cases, customers/users attend the review meeting and provide feedback to the development team, so reviews are also a means of customer/user communication.
Studies have shown that as a result of reviews, a significant increase in productivity and product quality can be achieved [Gilb and Graham, 1993], [van Veenendaal, 1999]. Reducing the number of defects early in the product life cycle also means that less time has to be spent on testing and maintenance. To summarize, the use of static testing, e.g. reviews, on software work products has various advantages:
- Since static testing can start early in the life cycle, early feedback on quality issues can be established, e.g. an early validation of user requirements and not just late in the life cycle during acceptance testing.
- By detecting defects at an early stage, rework costs are most often relatively low and thus a relatively cheap improvement of the quality of software products can be achieved.
- Since rework effort is substantially reduced, development productivity figures are likely to increase.
- The evaluation by a team has the additional advantage that there is an exchange of information between the participants.
- Static tests contribute to an increased awareness of quality issues.
In conclusion, static testing is a very suitable method for improving the quality of software work products. This applies primarily to the assessed products themselves, but it is also important that the quality improvement is not achieved once but has a more structural character. The feedback from the static testing process to the development process allows for process improvement, which supports the avoidance of similar errors being made in the future.
