The costs of quality are categorized into four types: prevention, detection (appraisal), internal failure, and external failure. Detection costs are incurred to find defects before the product is delivered to the customer. Writing test specifications is a fundamental activity in preparing for testing. Since the purpose of testing is to detect defects, the costs associated with creating the necessary artifacts for testing, such as test specifications, are classified as detection costs. These are costs of appraising the quality of the software.

B. Training developers is a prevention cost, as it aims to prevent defects from being introduced in the first place by improving skills.

C. Re-running a test to verify a fix is an internal failure cost, as it is a cost incurred due to a defect that was already found internally.

D. Fixing field failures is an external failure cost, as it relates to defects discovered by the customer after the product has been released.

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1. International Software Testing Qualifications Board (ISTQB®). (2018). Certified Tester Foundation Level Syllabus (Version 2018 V3.1). In Section 1.2.2, "Costs of Quality," detection costs (also called appraisal costs) are defined as costs for assessing the quality of the system. The syllabus provides examples such as "reviewing" and "testing," for which writing test specifications is a prerequisite activity. Conversely, "training" is listed as a prevention cost, "re-work" (including re-testing) as an internal failure cost, and "help desk" (related to field failures) as an external failure cost.

2. Pressman, R. S., & Maxim, B. R. (2020). Software Engineering: A Practitioner's Approach (9th ed.). McGraw-Hill Education. In Chapter 16, "Software Quality Assurance," the cost of quality model is detailed. Appraisal costs (detection costs) are described as activities to "uncover errors before they are delivered to the customer" (p. 453). This includes all tasks associated with testing, such as test planning and test case design (which includes writing specifications).

3. Sommerville, I. (2016). Software Engineering (10th ed.). Pearson. In Chapter 24, "Quality Management," the costs of quality are discussed. Appraisal costs are defined as "costs of the activities that are planned to discover defects in the software and system" (p. 728). This directly encompasses the planning and specification activities of the testing process.