Some test managers make a work breakdown structure based on a quality risk analysis outcome. In development projects, development managers create a work breakdown structure based on designs and requirements. These are called ascending or “bottom-up” estimating methods. Bottom-up estimates can be checked using top-down estimation rules. In companies where the processes have reached a sufficient degree of formalization, metrics such as functional points and projected lines of code produce top-down estimates. However, in most companies, test managers have to rely on simple empirical rules that compare the relative sizes of different phases of the development project. However, these empirical rules are inevitably inaccurate and should be applied together with breakdown structure, if accurate estimates of the project labor costs are required.

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One of the most commonly and widely used rational techniques for estimating software testing cost is the optimum ratio of testers to developers. You are recommended to download from the Internet two articles about methods based on ratio-estimates. One excellent paper was written by Johanna Rothman and its title is: “It Depends: Deciding on the Correct Ratio of Developers to Testers“. In it, Rothman presents an approach to finding the right ratio of testers to programmers, based on risk analysis, and gives three contrasting examples. She analyzes the risk areas associated with the product, the project, its processes and the working group. Product risks include increased complexity and large size.

Process and project risks include tight deadlines, the lack of an acceptable development process, testing and project management activities and the need for high quality. The risks related to the working group involve inexperienced testers, developers, marketers, project managers and other key project participants. The article describes the method of analyzing these risks to understand if an increment in the ratio of testers to programmers can lead to reducing the risks to the system’s quality. This approach fits perfectly with many popular specialized techniques. In addition to Rothman’s paper, one can read a thoughtful article by Kathleen A. Iberle and Susan Bartlett “Estimating Tester to Developer Ratios (or Not)“.