Assume you have some data related to confirmation testing during system testing of a past project. In that project 240 bug reports have been opened…

The total cost is calculated based on the number of times confirmation tests failed, which is indicated by bug reports being reopened.

- 80 bug reports were opened twice, meaning each failed confirmation testing once (80 1 = 80 failures).

- 10 bug reports were opened three times, meaning each failed confirmation testing twice (10 2 = 20 failures).

- Total failures = 80 + 20 = 100 failed confirmation tests.

- Total cost = 100 failures 3 person-hours/failure = 300 person-hours.

In the Cost of Quality model, costs associated with defects found before delivery to the customer are classified as internal failure costs. Since system testing is an internal pre-release activity, the cost of rework and re-testing falls into this category.

B. The cost calculation is incorrect. Also, these are internal failure costs, not external, as the defects were found before release to the customer.

C. The cost calculation is incorrect. The total number of failed tests is 100 (801 + 102), not a number that would result in 340 person-hours.

D. This is an internal failure cost, not a detection (appraisal) cost. Detection costs are for the initial testing effort, whereas failure costs are for rework and re-testing.

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1. Pressman, R. S., & Maxim, B. R. (2020). Software Engineering: A Practitioner's Approach (9th ed.). McGraw-Hill. In Chapter 15, Section 15.2.2 "The Cost of Quality," internal failure costs are defined as those incurred to correct defects discovered before the product is shipped to the customer, explicitly including "rework" and "failure analysis." The scenario describes exactly this situation.

2. Tian, J. (2005). Software Quality Engineering: Testing, Quality Assurance, and Quantifiable Improvement. Wiley-IEEE Computer Society Press. In Chapter 3, Section 3.3.2 "Cost of Quality," the Prevention-Appraisal-Failure (PAF) model is detailed. It classifies costs associated with defects found before shipment, such as debugging and re-testing, as internal failure costs.

3. MIT OpenCourseWare. (2010). 6.033 Computer System Engineering, Spring 2010. Lecture 20: Quality Assurance. The lecture notes distinguish between the costs of bugs found at different stages, reinforcing that costs from defects found during internal testing phases (like system testing) are distinct from and lower than external failure costs (post-release). This supports the classification as an internal, not external, failure.